Defense and contact is much improved, so I'm happy with that. The controller changes didn't strike me as too significant...I pulled off two alley oop passes my first game. The fancy pass scheme did take me a couple of minutes of adjustment.
All in all, the game is improved. It's just not improved very much, the same quirky bugs are still in it, and it's essentially a roster update with a LeBron mode. Few people outside of Miami will likely even stick with that mode to try it out, especially considering how absurd the scenario becomes.
For my purposes, which are the my player mode, it's still an awesome game. It just wasn't worth updating from 2K13.