Get ready to see an unusual pick for number 1. From worst to best:
6. Generation 6. Other than not caring for ORAS very much, I also did not enjoy the "feel" of these games. I can't explain how much the washed out aesthetics kind of drained my enjoyment and made the battles feel very... dull. I was also not fond of the fact that each area had a bajillion different Pokemon to catch. It was confusing and there were too many options. And I absolutely HATE Lumiose City. That place is not only confusing, but having listened to that music for so long being lost in it has driven me crazy and made me hate the theme too. Thankfully, the Pokemon designs followed in Gen V's footsteps for me. Being quite good, if sparse. (It introduced my favorite Pokemon, Braixen, after all) The small amount of Pokemon was bothersome for making a team made almost entirely of them. But hey, it added Mega Evolution. I liked that.
However, these games made me lose a lot of vigor and interest in Pokemon due to how... unfulfilling they felt in comparison to other generations. You didn't really have to put in the time and hard work anymore to train your Pokemon, even without the EXP Share, and the difficulty just danced all over the place. Then there was the extensive Gen 1 pandering. I don't dislike Gen 1. Not at all. But this just felt... really ingenuine and like they were tooting its horn far too much. Going as far as to include Kanto starters as an option during the main game and give you its legendaries as an option. The story being a step down from Black and White also grinded my gears quite a bit. Lots of potential, and a whole lot of nothing. I just want to forget Gen VI ever existed (other than the Pokemon designs), to be honest, and was absolutely glad that they were skipping a Z version to just move on to something new.
5. Generation 3. This was the only generation I skipped over entirely and I just really don't care about it at all. I don't hate it. I just... don't care. I loved the Pokemon designs, but not the Hoenn region too much. Also, it had a lot of weird idiosyncrasies. It refined the Pokemon formula, but that lack of a special/physical split in spite of seeming so much more advanced than what preceeded it really made it feel so primitive. It was just this awkward hybrid to me of Generation IV and Generations I and II. A teenage stage. Also, I kind of resent it for removing the more humble nature of Gens I and II. It just feels more... commercialized and mainstream. Just much cleaner due to being the start of modern Pokemon.
4. Generation 4. An improvement over Generation 3 and how I got back into the series after that hiatus, but I wasn't the most fond of it. The first half was... really lackluster to me. All I remember from these games is Cynthia. I also disliked or was "meh" about the whole batch of starters it had to offer, which wasn't a way to excite me. There were a lot of cool designs though. (Luxray, Staraptor, and who could forget Lucario?) And it finally introduced the special/physical split and Wi-Fi, two features that changed a lot. Further, HeartGold is one of my favorite games in the series. If this generation had just HGSS, I'd rate it higher. But I have to put into consideration the MAIN games, and I just didn't enjoy my time with Diamond as much.
3. Generation 1. Another one I kind of skipped over, having started with Gen 2. It's primitive, it's clunky, it's goddamn slow, and the graphics are ugly as sin. (Not counting Yellow, which improved them slightly) Also, too many Poison-types and a lot of bland designs that I just kind of forget exist. (Farfetch'd, Pinsir, both of its fossils) But it has a charm to it, I won't deny that. It feels much more sincere than the other generations, because it doesn't know what it wants to be yet, and it doesn't know that it's going to be a big hit. That sincerity and humbleness makes it a more refreshing experience. It's just... really odd and that's entertaining in its own way. I suppose I could call it "quaint."
2. Generation 2. Biased here, I know. It was my first generation, after all. I've played through Gold and Silver so much, they're the only Pokemon games I know by heart. Honestly, I'm not even fond of the Johto Pokemon too much. It introduced even more bland and forgettable ones. (Sunflora, Quillfish, Magcargo) But it had some of my favorite cross-gen evolutions as well, and ones that fit in perfectly with the older designs. (Umbreon and Espeon especially.) And it was just... so weird and quirky. It is unlike any other Pokemon game released after Gen I, because it is a direct continuation. Its Pokemon aren't redundant for the most part and it isn't afraid not to follow series "traditions" that I find tiring. There are no fossils or Pikachu rip-offs. The fact is as well, it improved upon its predecessor immensely. It added such key features as genders, breeding, splitting items into different sections in the bag, etc. And of course, TWO regions. The main billing that people still won't get over to this day. I find these games to be a masterful series of sequels. These are how you improve upon a series whilst still keeping the same feel of it.
1. Generation 5! The ever unpopular Generation 5. Yes, they surpass my first games. Why? Well, because when I play a video game, there is one thing you can do to really make me like it. That's making me care about its characters and story. Now, Black and White aren't Final Fantasy level. These aren't the deepest or best stories ever told. But for a Pokemon game? They set the bar much higher than what I had seen before. This was the one time a Pokemon game surprised and impressed me.
The graphics and sprites also had this very fresh and lively feeling. They moved in a... somehow more fluid way than the models. I loved the interface. And some of the human designs were even INTERESTING to me, which rarely happens. (Bianca, Elesa in BW2, Alder, Cheren, Professor Juniper, N) Speaking of humans, the human characters.. they actually had a personality beyond a few sentences. They really grew on me, particularly Bianca, who I could relate to because of her father disapproving of her journey.
Then there was the music. The story wouldn't have had nearly as much as an impact if I hadn't loved that phenomenal music. I found most of the tracks to be very memorable. Elite 4, legendary battles, gym battles, all so full of energy. And then there was that one piano song that plays when Bianca is speaking to her father... that was the most emotional track I've ever heard in a Pokemon game.
These games were just so odd compared to the rest, and that's what I appreciate. Oddity, breaking norms and patterns, standing out. They didn't let you use older Pokemon; they forced you to use entirely brand new ones. (Admittedly, some of those were rip-offs of older ones, which I don't like so much. But I still appreciate the feeling of a reboot) Other people, they complained and complained about this. Me? I loved it! Everything new, everything fresh. (Was quite disappointed when brought back the older Pokemon for BW2) Also, there were loads of great designs. Not just the trash and ice cream Pokemon as others like to fixate on. But things like Mienshao, Zoroark, Excadrill, Serperior, Scolipede, Lilligant, etc. It was really difficult for me to decide what to have on my team.
And it introduced my favorite legendary of all time. Reshiram. Look at that thing. It is so beautiful and perfect, I can't explain to you how much it pleases my aesthetic senses. A pure white graceful bird/mammal/dragon hybrid. If these games weren't my favorites, I'll be honest, I wouldn't have ranked Gen 6 as low as I did. But they gave me enthusiasm for the future of Pokemon, which set me up for massive disappointment in the current gen. I only hope that Sun and Moon emulate the parts of Gen 5 that I absolutely love.