>>31685985During maingame, I'd say it's definitely the story and the slight changes to the formula that made me enjoy it much more. While the cutscenes were excessive, I enjoyed them. I can get to battling any time, so I don't mind being stopped every now and then. The Trails, while nothing special, gave a slightly different goal than just beating 8 Gyms. These two outweigh all the flaws by a good amount for me. Removal of HMs and such just add to that.
As for why it's keeping me still interested even after the story is over, I'm not sure how to put it into words, to be perfectly honest. There's not a whole lot of content, but what is there is fun? After I finished BW, for example, I just stopped playing after exploring the new areas. There were things to do, like Subway, but it just felt boring, even though it's pretty similar to Tree. Same happened with DP and RS. XY kept me going a bit longer, because I really enjoyed completing the Pokedex in them, but it repeated with ORAS.
SM has managed to somehow make me not lose interest. Maybe it's just the graphics, which help immerse easier than previous games. Maybe it's because some things are easier, like Breeding. Maybe the story just made me attached to the region. I can't pinpoint a clear reason, but it is definitely keeping me around.