King of Fighter XI is the best Kof game ever!! hands down!!
Kof XI excels in everything, from gameplay to the various modes at your disposal, yes its graphics are not as good as tekken or street fighter third strike or whatever, but for anything else is the best 2D fighter on the PS2 ever and, for me, the best fighting game I have ever played, the character roster is huge, lots to unlock, the last boss can be cheap but its such a satisfaction beating him, no other game has left me with that sensation yet.
The challenge mode is crazy hard, but it can be cleared, if I did it anyone can, I had to check out youtube videos for some of the challenges I'll admit, but you can do them, don't let the difficulty put you off, with practice you can beat the game.
As for the story, is the best I have seen in a fighting game, confusing at times, but if you follow through it, you 'll be gripped as well as I was, its like playing through an anime movie.
The super cancel and the dream cancel are hard to grasp at fist, but with a little practice you ll be pulling off combos that will freak you out and add a lot of depth to the gameplay in my opinion.
In conclusion, Kof XI is a game any PS2 owner has to have in their collections, especially if they enjoy fighting games, I hope that Kof 13 will be more in line with this one whenever it comes out, forget any other fighting games out there, King of fighters XI really is THE king among fighting games.