From Bulbapedia, the community-driven Pokémon encyclopedia.
...Gliscor's back, Cyndaquil evolved, Brock's leaving.
...so why am I not happy?
Let's examine the past for a moment, shall we? Let's go back and look at Ash's party over the course of all of the regions. Each time it is changed, I will note the episode number.
Ash starts with Pikachu. Oak gives him a Pokédex and five Poké Balls with which to capture Pokémon.
Ash captures a Caterpie. This is why Ash's Seaking is notable: Ash caught it.
Ash is an idiot! He sends Caterpie into battle against a Pidgeotto! True genius. Glad he's matured since then... for real. He calls Caterpie back because Misty tells him he's an idiot, sends out Pikachu, and then captures Pidgeotto!
Team Rocket appears! Pidgeotto is defeated, Pikachu is sludged, and only Caterpie remains. It SOMEHOW manages to kick both Koffing's AND Ekans's asses. Then it evolves!
Ash gets into his first official battle... with some idiot Bug Catcher. He misses catching a Weedle. He loses Metapod to some Beedrill, but manages to get it back. Metapod is injured protecting his stupid ass from a Beedrill, but then... Butterfree comes out!
After beating the crap out of two Gyms (not really) with just three Pokémon, Ash encounters a Bulbasaur. Misty demonstrates her lack of knowledge about Pokémon NATIVE TO HER OWN REGION. Ash captures Bulbasaur after it tries to kill Misty for wanting an Oddish.
Some stupid asshole releases his Charmander and leaves it on a rock. Dammit, why does Ash continually get pre-owned Fire-type starters?
A bunch of asshole Squirtle are terrorizing a town. No one is doing anything about it, so Ash has to stop by and lay down the law. Great job being a police force, Jenny. Ash eventually helps, then captures the leader of the Squirtle Squad.
Ash has only six Pokémon at this point, and Gary has like, 20,000,000. So Ash decides to catch one more: A Krabby. Then the ball disappears and he wonders where the hell it went. Looks like SOMEONE wasn't paying attention... So now, Ash has 7 Pokémon, with a Pokédex listing of 9. And he's already going for his third badge.
Ash actually trades something! But it's the first Pokémon he caught. Good job, moron. You know you get attached to those. I know I was in Diamond, with Gruntilda.
So then he trades back. Ah well, at least now he has 10 in his dex listing.
And then Ash does it again. He releases Butterfree! It was, like, his best Pokémon... and that's saying something for a Butterfree in Generation I.
Just to make it legal to have Haunter with him, Ash released Butterfree. That's the ONLY reasoning I see for it.
But then he gives it to Sabrina. Genius!
Oh, but then here comes my favorite episode, just because it demonstrates completely Ash's lack of maturity.
And then the ass releases it, because the guy wants to make it a "real P1 champion". Dude, it JUST KICKED YOUR HITMONCHAN'S ASS TO BE THAT ANYWAY. Ash demonstrates once again that he's a complete idiot.
Ash demonstrates that he doesn't know the difference between a streaker and a stalker. He captures Muk, which later proves useful in League matches... but only those.
Then he Oaks it.
Then Ash captures 30 Tauros when trying to capture ANYTHING BUT. Idiot. We never see this because the US is afraid of guns, yet we're like, the only country on Earth where citizens are free to carry one...
Then, for the first time since Metapod evolved, something of Ash's actually evolves... and becomes an arrogant ass.
And then Charmeleon evolves...
...and Ash finds an egg. Generation II is encroaching...
And the egg hatches... AND MISTY STEALS IT. What the HELL, man. She then proceeds to baby it and it does nothing useful at all until the Orange Islands, then for some reason stops being awesome and sits there in her arms episode after episode until AG045.
Ash hasn't captured anything in FOREVER. But he decides to ACTUALLY USE KRABBY.
And so it decides to kick ass and evolve. They were seriously just looking for a reason to say it didn't suck.
And now, Ash looks like he's doing good. He's winning his way up, with TOTALLY UNEVOLVED POKÉMON. He Oaks Kingler for Muk.
And then he blows it because Charizard doesn't want to battle. Idiot. BUT HEY. Now Pidgeotto finally evolves!
But he releases it. What the hell, man. I'm surprised he didn't release Charizard-- oh wait.
And that's the end of Kanto!
Ash begins his journey in the Orange Islands by falling for another one of Team Rocket's tricks.
Ash then becomes a hero and saves a Lapras from a bunch of idiots who are beating it up. Tracey invites himself along.
Exactly ten episodes pass, and Ash makes another capture. Now his party is full again, and remains that way for more than three episodes!
And... Snorlax decides to be a lazy ass. Wonderful. So Ash decides to go with "beginner's luck" once more and brings Tauros in return for Snorlax.
AND ASH WINS. WHAT.
And now, the end of the Orange Islands saga... and Ash releases Lapras.
Ash, Misty, and Brock head for Johto. Ash dumps off Tauros at Oak's to be with the rest.
Ash starts off in Johto, and Team Rocket has stolen a Totodile. But he gets it back for Professor Elm.
Ash catches a Heracross. Heracross starts pissing off Bulbasaur.
Ash catches a Chikorita. Now he has two Grass-types, and continues to have them for much of the saga.
Ash releases Charizard... sorta. He basically says "go live in the Charicific Valley and train", not knowing that Charizard's definition of "train" includes Charla.
But not to worry... Ash isn't totally screwed against the Bug-type Gym Leader because he has nothing that weakens Bugs... because he catches a Cyndaquil!
And Ash dumps Heracross off at Oak's for a Tauros, because he has a million.
Ash asks Oak for Heracross back, but Oak wants to keep it there (excuses, excuses...) so Ash just sends Tauros back.
...and then... he releases Squirtle. Or more, lets it go help the Squirtle Squad.
And here we are, at the 151st episode... Anything special? Well, Ash gets a Totodile!
So what now? Ash has everything he had in Kanto... Pikachu... Grass... Fire... Water... what's left? Flying! And he gets something extra special this time... A shiny Noctowl!
A while has passed... Ash wins two competitions with a Seaking and a Beedrill, both of which he does not keep. Now, entered in another competition, he leaves Noctowl at Oak's for his sumo champion.
Then he wins, sends Snorlax back, and goes on his merry way...
Chikorita, being his most-used, finally evolves, being the only one to do so in Johto.
Oak's got a problem at his lab... and he needs Ash's Bulbasaur to fix it. So Ash sends Bulbasaur back... and all that remains of Ash's Kanto crew on his team now... is Pikachu.
Ash wins a race, and gets an egg! Let's see if they do something right this time...
Ash's recently-obtained egg hatches into a Phanpy! Late comers abound.
Ash has decided to go to Hoenn, so he dumps everyone but Pikachu off at Oak's, in order to better represent the incompatibilities of Gen II and III.
Ash arrives in Hoenn. Team Rocket steals Pikachu, so he's got nothing else. Guess he'll have to send out ??????????...
But he gets Pikachu back quickly, starts off with May, and heads toward Petalburg!
Ash makes his fist Hoenn-region capture: Taillow! He's getting into a pattern...
Uh oh... more starters. Everyone thinks that after this, Mudkip just has to be Ash's.
But no. Ash is only going for ONE starter from now on, so he'll have to get a different Water-type...
...and a different Fire-type... Ironically, even though Corphish can evolve, it never does, and Torkoal can't anyway... Methinks Ash is giving preferential treatment to one of his three major types...
...yep. I was right.
Buuuuuuut, making a return trip from Kanto (guess what this references...) is Bulbasaur! And it likes May's Bulbasaur... let's just hope he doesn't use Leech Seed...
...and then he sends it back. Thankfully it didn't have a chance to use that move.
Hey, wow, before the end of the series, too! The writers know what they're doing now!
Full party again, for the first time in a while.
Full party and almost everyone has evolved, too... they really know what they're doing now!
And that's it, Hoenn's over!
BUT WAIT. FRLG and E have just come out! You know what that means! FILLER SEASON!
And so, Brock and Ash leave May and Max in Hoenn and it's time for them to go...
Back to Kanto
Ash starts off again from Pallet Town, now going to see all the stuff he didn't see the first time he went through Kanto (in 80 episodes!), and to take the Battle Frontier challenge. And to start off, he dumps his crybaby at Oak's for a Johto Pokémon that didn't get much screentime...
And it's not Cyndaquil. DAMMIT.
Plus he dumps his iceball.
So Phanpy finally does what it was supposed to... And of course, Ash again has something that he's seen before. Donphan!
And again we have one of Ash's Pokémon reaching a second evolution... and this one LISTENS.
Ash gets his hat stolen... but Aipom gives it back and Ash doesn't scream at it! GASP. Then he catches it.
And now, the Battle Frontier is over, and Ash wants to go to Sinnoh. May goes to Johto. Ash dumps EVERYTHING off with Oak except Pikachu, ONCE AGAIN.
And now he's off, all alone again... but this time, it's to Sinnoh!
But guess what! A stowaway is aboard the ship! And it's Aipom! Guess Ash isn't going to Sinnoh alone with Pikachu anymore.
Ash again begins his pattern, catching the native Normal/Flying Pokémon.
More pattern-driven goodness. At least this time, unlike in Johto, it'll help him in his first Gym match.
An early evolution! Last time one of these happened so early, it was Kanto!
And... that's a looooong time between captures for Ash. And Chimchar's... exactly like Charmander, as far as capture method.
Wait, what. Ash and Dawn trade Aipom and Buizel? Thanks a lot, Zoey!
Another out of the blue capture... Ash gets... a Gligar. I mean, everyone thought he'd get Hippopotas, but that fell through... so he gets a JOHTO Ground-type?
Well, so much for having a Gen II Pokémon, Ash. Gligar's predicted evolution happens, and now he and Paul share a species.
Finally, Turtwig evolves, and proves it's not just a Bulbaclone.
Look at that, another Pokéringer, and Ash's bird evolves into its final form. At least he didn't release this one!
And the faceoff finally happens. And Monferno arrives as an evolution. When's the Infernape?
...Ash you MORON. THEY ALWAYS SAY THEY'LL HELP YOUR POKÉMON BECAUSE YOU ARE A GULLIBLE FOOL WHO WOULD GIVE EVEN PIKACHU AWAY.
Ash gets a damn pseudo-legendary... yaaahoo. It had better f'ing evolve.
Monferno becomes Infernape. But it's not an asshole like Charizard was.
Grotle becomes Torterra. We all saw it coming. Thanks new opening. Too lazy to do a changing animation this time?
Ash brings back his parties of the past from Oak's. And... promptly loses them in the forest. Honestly. Then he finds everyone except for Cyndaquil, who Team Rocket attacks. And Cyndaquil does what we have all been waiting for since JOHTO. It evolves into Quilava!
Oh, just another episode, and wait holy shit GLISCOR?! It came back!? A Pokémon Ash RELEASED like an idiot came back?!
I demand a fricking recount. Bring back Primeape!
Yay Sinnoh League. Yay not really exciting. Yay Ash beats Paul and gets to face a cheater with a fricking DARKRAI. You can't enter it in the Battle Tower. That's not legit. No legendaries. It's bull. And we're of course not going back to Johto, even though glorious-ass Kanto got a return trip in AG.
And of course, this means Totodile got screwed over. THANKS, WRITERS, FOR GIVING US FIFTY FUCKING FILLERS BETWEEN CANDICE AND VOLKNER. Now we'll never resolve Ash's journey at the Bell Tower, never see that fucker Petrel, never get rid of Team Rocket, FOR GOD'S SAKE. They're planning on DUMPING BROCK at last in BW, but TEAM ROCKET IS STILL AROUND? Goddamn! Give Plasma some actual plot, unlike the past four generations where you completely fucked up on any trace of coolness Rocket, Magma, Aqua, and Galactic had! I know, I know, kids' show. Advertising the games is the #1 point. But MY GOD, we got our Kanto and Johto remakes. We're not going back. Leave them to the past. Move forward to Isshu. We're starting over. I'm ready for it. No more Zubat, instead we have Koromori. No Drowzee, instead we have Munna. I'm cool with it. Cyndi Quil returned to my side for one last hurrah, but now I'm ready for my firepiggy, and I'm not looking back at Generation I, II, III, or IV, and wishing for the good old days in Kanto, Johto, Hoenn, or Sinnoh.
Sigh. Well. Better get to work on the teams for Dent and Iris.