Write your thoughts on every main series Pokémon game
I'm not including remakes and I'm combining upper versions with the base versions, because I'd be here forever, but it's up to you if you want to list them seperately.
RBY
Gen 1 has a unique atmosphere that hasn't been replicated in any of the subsequent games, even the remakes, mostly due to the hardware it was developed on, but I think GAME FREAK used it very well to make Kanto feel very urban and gritty. If you go back and replay them, the best way is to forget that anything after Mew exists, and really immerse yourself into the world. The wacky sprites makes the Pokémon feel like traditional JRPG monsters.
GSC
Probably my personal favourite, except maybe the remakes. I don't even have any nostalgia for Gen 2, I was born after they were released, but when I first played them I was very impressed with how much more polished it felt compared to Gen 1, and I loved how it built on the foundation of Gen 1, improving and adding new mechanics, and introducing features that really immerse the player, such as the day/night cycle, timed events and being able to take the numbers of trainers you meet along your journey. Like Gen 1, GAME FREAK utilised the hardware well to make Johto feel very rural and homely, with all the warm, saturated colours and beautiful spritework.
RSE
This was the start of the modern era of Pokémon in my opinion, and RSE has a lot of strengths and weaknesses, but overall, the positives vastly outweigh the negatives. Hoenn is the most well-designed map in all of Pokémon, with there being stuff to discover in every corner and different areas interconnecting naturally. RSE is fun to replay just for the feel of exploring the region alone.
DPPt
Despite viewing the Sinnoh games as some of the weaker entries in the series, the games have a very nice atmosphere that combine Johto's traditional and rural feel with Kanto's more modernized feel, and yet it still feels very natural and keeps the game feeling fresh as you progress through it. The Sinnoh games definitely have the best soundtrack out of every main series game, and that alone gives it a high enough rank in my book.
BW/B2W2
I can never get into the Unova games for some reason, but I see why they're so beloved in the Pokémon community. BW being limited to only its new roster of 156 Pokémon was such a great idea and I wish GAME FREAK would do it again. just for the novelty. It was the first game to have unique music tracks for each town and city, which made each location feel a lot more memorable. The linear and railroaded progression of the game, despite being a flaw in some peoples' eyes, made you appreciate the locations more, rather than just rushing through them. B2W2 is arguably the most content-filled Pokémon game to date, only rivalled by HGSS.
XY
These were the last games I played completely blind for my first run, which gives them a special place in my heart. I remember being mind-blown from seeing the 3D models for the first time. Though many look back at these entries with negativity, I can forgive them for their flaws and forgetability just for taking the neccessary steps to pushing the franchise forwards. Other than that, there's not much else to say about them. They were neither spectacular nor garbage.
SM/USUM
I fondly remember the hype season leading up to SM, and I really enjoyed playing through them for the first time. Visually, they looked amazing for the system they were on, and it really felt like you were on a holiday in Hawaii. The locations and music were great, and I think these games introduced the best set of new legendaries, with Solgaleo and Lunala as the box legendaries, the Tapus, and the Ultra Beasts all feeling super unique to eachother while being integrated into the world and story very well. I can't ever see myself playing these games ever again (for obvious reasons), but I will always remember my first experience with them.
SwSh
These games weren't great, to be completely honest, even with the excitement of playing a new generation of Pokémon games for the first time. They felt like a step back in many ways. The Gym stadiums were awesome, it was always how I imagined Gym battles to be like as a kid, but other than that, I can't really say anything else positive about them. I will say that the new Galar Pokémon felt really cohesive as a new set, like they just all work well together to enhance the feel of the region, but I'd still rather pretend these games never happened.
SV
This was the most fun I've had in a Pokémon game since I was a kid. SV took a neccessary step to progress Pokémon into modernity, but I couldn't not look past the broken and overall unpolished feel of it all. LA was a much higher quality game in my opinion, but as far as main series goes, SV is easily the best game since HGSS, just for taking its chances and trying something new, even if it wasn't fully cooked. With just a few more months in the oven, SV could've turned out great.