NBA 2K9 had been the best basketball simulation and I believe it still is.
The graphics been improved. Now, players have sweat on their forehead except for Andrew Bynum; 2K just transferred the 2K8 version of Bynum onto 2K9 except they gave him vivid age lines; GOSH 2K, he's only in his early 20s! With sweat, the players don't look bland anymore. Courts are shinier, making them look more real, but the blurriness of the logos on the courts and on the player's uniform are a total let down(go to the 2K forums and you'll see what I mean, many complaints on that). Though the cut scenes are great, players have too many jaggies and their movements are very robotic-like. I would like to see more action replays in-game.
On to gameplay, some good and some bad. Iso-motion is horrible and way too complicating. There is no stopping the CPU in paint, they just get it in even if you have your hands in his face. Manual game slider is required to experience the whole simulation because it is too easy for you and the CPU to score on default. Many people been complaining about 2K eliminating the 2K camera view. I don't really use the 2K view because broadcast looks way real, but I hope 2K release a patch on adding it so people can stop whining about it.
Black top has not gone anywhere though the location of the Slam Dunk Contest's changed. Association is a lot better this year. Now with player ambitions, in-game NBA.com, three team trades, etc.
Overall, NBA 2K9 is a solid game that beats all other basketball simulation video games. Online is really crap and I can only hope 2K fixes it in the future. All people who have NBA 2K8, rent it first because you may regret buying it, but I was going to get it regardless.