The PSP version of 2K11 is a decent portable effort, but fails to innovate or grow the franchise.
Keep in mind, I've never played NBA 2K10 for the PSP, so I'm judging this game based on what it is.
The first thing that any player familiar to the NBA 2K series will notice is that the PSP version of NBA 2K11 borrows a lot of the pre game introductions from older games in the series such as NBA 2K6. In fact, upon closer inspection, it becomes painfully obvious that NBA 2K11 IS NBA 2K6 with updated rosters. The association mode has none of the features which have been improved in recent iterations, the gameplay is a lot simpler, but still fun, which I guess means it is reasonably well suited to the portable platform, and the only meaningful edition to the game is the My Player mode, which is so half assed and broken its not even funny.
However, with the huge deal they've been making about the return of Jordan in their ad campaigns, you'd have figured they would have at least TRIED to implement the Jordan Challenge mode into the PSP version, but thats a no go. Jordan is in the game, but he can only be used in practice mode and can be used in the street mode along with a bunch of other veterans. This is a real shame, because the Jordan Challenge is definitely a mode that could sell the game to someone who doesn't annually buy NBA games.
Another thing to note, is that in order for the game to even remotely resemble realistic basketball, a ton of tweaking will have to be done, not just to the game sliders, but to the player rosters as well. I think what ended up happening here is that when the attributes were being transferred over from the console versions, they weren't converted into the ratings formula NBA 2K6 uses (the minimum overall in 2K6 is 50 as opposed to 25 in NBA 2K10).
The rosters are also horribly out of date, Tracy Mcgrady, Delonte West, Shaq, and a host of other players are either on the wrong team, or are still in free agency, despite being signed for months, several rookies are missing from the rosters as well, and because its the PSP version, its pretty unlikely we'll see a roster update from 2K any time soon.
Graphically, NBA 2K11 isn't bad for a PSP game but it certainly doesn't look good either. The frame rate is pretty smooth, which is nice, but the game could definitely do with a bit more polish. In a lot of cases the cyberfaces look like they've been painted on the heads of the players. There are also a lot of inconsistencies with how the courts look, but this isn't really unusual for a handheld sports game.
One plus has to be the music, the NBA 2K series has generally had a pretty nice variety of music, and while I personally don't like the selection as much as NBA 2K9 or 2K10, the music is still pretty good. The commentary on the PSP version is also pretty good. It doesn't come close to the current gen versions are, where the commentary may very well be the best part of the game, but its more than passable and usually keeps up with the action.
So, overall, NBA 2K11 on the PSP isn't a bad basketball game, and as of right now, with NBA Elite 11's fate up in the air, if you're a basketball fan, and the PSP is your only system, then this is probably worth the 20 bucks. However, if you have an Xbox 360, PS3, or even a capable PC, you'd be doing yourself a favor buying one of those versions instead.