I always will love Gen 5.
the main thing was that it locked the old pokemon so you'd HAVE to play with the new 150 and start a new adventure with a new team. I always feel so disheartened when I see people so eager to transfer their top tier pokemon from old games into the new ones solely because they don't want to have to bother dealing with the new ones or even giving them a chance. I like how gamefreak pretty much was like "play the new pokemon. don't like it? beat the game. don't like that either? well, go fuck yourself"
also, I don't mind how they dropped the rotating seasons in gen 6. Unova had a more diverse landscape and different terrains, so differing seasons wouldn't really matter in more snowy or desert areas.