NBA 2K is an annual purchase for me, though on the PS3. I'm more of an offline association mode player, so unfortunately they don't make that many changes year to year that help me. Player ratings are generally weak, but the gameplay is great.
Some consistent bugs that they never manage to stamp out are annoying as well such as my favorite team's scout making $8 million of the $10 million allocated to your coaching staff. Every year it takes 3 seasons before that awful contract expires.