Here's what I remember>DP well-liked>Platinum really liked>HGSS adored>BW being a mixed bag>B2W2 getting a lot of love>XY having people love the online but dislike the main game>ORAS disliked>SM as disappointments>USUM as disappointments
As someone who was on forums for all of the Japanese releases. Every game gets love as it's first released, even USUM have people going through every new aspect. People like seeing new Necrozma forms and new abilities and Pokémon and moves. But Pokémon is weird because there are plenty of nostalgiafags who think their childhood game was perfect. Not many people who actually try and look at each game critically. My childhood game was Silver, so I have a lot of love for Gen II, but I can still see plenty of flaws with it. The DP hatred is what really confuses me. Gen IV had an amazingly strong start with them. Platinum was numerous small improvements that added up to a perfect third version, but DP was a really solid foundation to begin with. Yeah, they're the slowest of the mainline games, but they do so many things right. They had several in-game story events for Mythical Pokémon, which RG, GS, RS, XY, and SM don't. BW had Victini, but that was it.
To me, BW is on par with FRLG. There's stuff to like but it doesn't do enough to stand out. The one thing that it received a lot of praise for at release was its heavier focus on story which was cool at the time for Pokémon, but it's burdened the series since. There's stuff I admire about XY, and every game since has only made me appreciate it it more in comparison, but I don't think it's a better game than it used to be. A guy with all his limbs broken still admires the guy with broken legs.