Just get 2K12. It's only $40 new, and you can find it for somewhere around $20 used. The game is much deeper, and the AI is vastly improved. The CPU actually reacts to jab steps, stepovers in 2k12. There is also more of a "live ball" effect that makes users think twice before dribbling into heavy traffic.
Not to mention the more advanced dribble moves(isomotion chain moves like crossover-spin, crossover-behind-the-back), much deeper post game(aggressive drives, less effective face-up, traveling violations for excessive up fakes, ability to anticipate moves and their direction), deeper My Player mode, more in-depth player abilities (ability to create your own jumpshots), and 2K's ability to update cyberfaces through roster updates.
If you're one who is really into realistic gameplay and stats, the devs have fixed the issues with low offensive rebounding and low off-ball foul numbers. They also finally fixed the way that steals and rebounds are counted this year (rebounds were formerly were not counted on blocked shots, steals were rewarded to the player who retrieved the ball after the initial deflection).
The responsiveness online in 2K12 is a bit of a step down from 2K11, especially with icon passing. There is also the removal of Online Leagues, Crew, lobbies, and custom sliders that may detract from the total online experience, but the game is still enjoyable online. The infamous spin-dunk cheese was nerfed this year, along with the excessive lead pass, largely due to the new "live ball" effect.
One of the biggest disappointments for me was the inability to run a season with the authentic 66-game schedule. That goes to show how solid the game is overall.