While I'm certainly not against enhancements to the visuals, that wouldn't be the biggest complaint for me as far as the game's freshness. Even if we're talking about the animations rather than the lighting, atmosphere, or whatever, I still think that the quality is satisfactory at the very least. Again, any enhancements are welcome, but I don't feel that those are the biggest issues.
For me, the bigger problems as far as the game feeling dated are concerned would be legacy issues with the gameplay. We have the new Eco-Motion engine, and the responsiveness of the controls has improved over the past couple of games, but there's still some clunkiness from time to time: hitches when trying to sprint, a feeling of running in mud, and so on. There are also still balance issues with the game, where the CPU remains competitive somewhat artificially. Having played a lot of 2K Pro-Am lately, better balance also needs to be achieved in User vs. User games as well. A starting five of 90+ Overall players throws everything out of whack, and the nerfs they tried in the patches tended to end up hurting lower rated players more than they evened up the playing field, while still allowing for some cheesy play.
While I'm normally against massive overhauls to the controls every year, I'm also thinking it might be time to re-evaluate some of the approaches in 2K. I've always felt that NBA Live has had a more intuitive approach to its controls, even when the depth hasn't been there. 2K has the depth and that's fantastic, but there are times when the controls still feel a bit contrived, especially for advanced moves. The Shot Stick is still pretty hit and miss for me as far as being able to pull off the exact move I want, and the fact that it's combined with dribbling controls can make things cumbersome. I'm more a fan of right stick dribbling than right stick shooting, though I do get the benefits of the Shot Stick. I must admit that I don't have any specific ideas for how I'd change it, at least not off the top of my head, but I feel like something has to be ironed out there.
Same goes for some legacy issues with the grading logic in MyCAREER (and now Pro-Am). There are still some of the same glitches, to say nothing of the approach of focusing on severely punishing mistakes than rewarding consistently good play. I'm sure there has actually been work done under the hood there, but to be honest, when I do see some of the same old problems occurring, it feels like nothing has been done with it for at least two or three years now.
Like I said, visual enhancements are important in their own right, but even if you fix all that up and make the game look nicer, you're still going to run into issues with the gameplay and features. I would suggest that fixing some of these things are easier said than done, but it doesn't make it any less frustrating when certain issues have annoyed us for a few years running.