(Counting remakes in the gen they were remade in. ex: FR and LF in 3rd, HG and SS in 4th)
1st gen: Ah, the one that started it all. Yes, you had your share of glitches and OP types and you may not have held up as great as others had hoped, but to start it all...it was pretty good.
2nd gen: Loved this gen! My sister and I played it so much that we memorized every time event within it. I just really enjoyed this gen.
3rd gen: RSE: Ok this is where I started to get a little...worn out? Is that the word? For a while, this was my least favorite gen, but I think it was because that they stepped up their game in terms of difficulty and strategy. Playing now, I really enjoy it b/c I see that it allowed me to adapt to the new playing style changes. So I would say it did a lot of good. However, it dropped day and night cycles, animations in the sprites (they put them back in Emerald), LOTS of water, but I realized they were going for a more tropical environment, and...lots of trumpets. Dat trumpet, they say when pretty all the music had some form of trumpet in it so Hoenn seemed to have the same sound as it were.
FR/LG: A bit underwhelming, but I liked the new content they added, well, not really new, just stuff they didn't include in the first release. Overall, similar problems with R/S
4th gen: D/P/Pt: Battles SO SLOOOOWWWW, really glad that they fixed that in Platinum. This could be where pokemon slowed down a bit in terms of everything. Pokémon wasn't as popular as it used to be, they were bringing in new evos to old pokemon to draw some of the old players back, the plot wasn't that great (but when has pokemon ever been about the plot, really?). Climbing Mt. Coronet was probably my least favorite part of the game, but they were things I discovered after the main game that I thought was mind blowing. Mainly finding Sendoff Spring without knowledge of what it was or why it was there. It's not my favorite generation, but it brought one of the best innovations: The physical special split.
Hg/SS: Great remakes, but at the same time, they felt a little...rushed, but I don't know. I still thought they were pretty good since they fixed a lot of thing that were wrong in the first games. The pokemon walking behind you was a nice touch, but I'm not super upset that they got rid of them.
5th gen: Oh. OH. Um...give me a second....Ok, I'm good. I'm going to be completely honest and say that I hate gen 5, but let me explain.
What I liked about gen 5: a select amount of the new pokemon like the Oshawott line, the Snivy line, Larvesta line, and the Driburr line (there are more, I just can't remember all of them off the top of my head), now that I've thought about it- 5th gen's plot is pretty legit, a bit laughable at times, but I like the step up here, and N.
What I didn't like: The LONG time you had to wait for pokemon to evolve and the fact that the pokemon was extremely weak until level 49 or in the 50s, the fact that there were just a flood of pokemon that weren't great (I would've been fine with it if they didn't limit your pokemon selection...speaking of which), the fact that you couldn't use any previous gen pokemon without trading, the rivals were bland, the champion was bland, the map appeared to give you freedom but was horribly linear (in it's defense 6th gen is pretty linear too, but imo 6th gen handled it better), the level spike in the wild after the E4, the 'twist' in the villain arc with Ghetsis, the lack of adding anything that was really innovating (Triple and Rotation battles were clunky and unnecessary in 5th gen), and the overly pixilated sprites.
BW2: Similar problems, but the addition of adding in pokemon from previous gens fixed a large portion of it with me. Wasn't...as linear, but still pretty linear. It felt kind of boring, that was probably just me though, but I was shocked at how bored I was when playing this game.
6th gen: Whew, back into positive territory. Let's see: Starters were great (can you say, a change in typing? XD LOL), the region was fun, there was the lowest amount of pokemon added in history, but was brought up with the largest regional pokedex in history as well, which masked the small selection very well. The 3D sprites were a great addition and brought more life to the game. Pokémon Amie wasn't really necessary, but it was fun to play with the pokemon I caught. The rivals were bland again (more does not necessarily mean better). It just felt like a breath of fresh air and that I was never done exploring something, which was kind of fun for me!
Sooooo, overall, I think the pokemon games hit a slight rough patch in 3rd and 4th due to the fanbase, but weren't bad, 5th gen was gosh awful, and 6th gen was a step in the right direction imo. So I think only gen 5 was the only instance of the generations being 'worse'.