Xbox One here, bought it digital tonight and it's almost done downloading. I got in a game of Spurs vs. Heat and can immediately tell an improvement in gameplay over 2K14 on the same console last year. Movement really feels a bit more responsive, too, I feel like I can better get my guy where I want him when I want him.
I've seen lots of comments of it not showing installation progress, I'm having no problem seeing that. It showed it on the title screen until I pressed A, then it also showed in the lower-left during the entire game I played.
As far as the graphics, I think they look as good as last year (yes, I'm aware of my username here, no need to point it out). Of course, I'm not comparing them side-by-side, I don't see the point in that. They either look good or they don't. I can tell a lot of work has been done on the eyes but what's weird is that some players in that Spurs/Heat game really benefit from the eyes and others look like a deer in headlights. There's not much eye movement either, so it's like they're just staring ahead. Odd as it is to say this after typing that last sentence, they do look a little more "alive" this year than last.
I haven't dove into MyPlayer yet, which is really the only thing I play, that will come tomorrow night. Just wanted to post and say that so far, things look good to me, not all the doom and gloom that I've read thus far.