Facebook's App Center has a distinct advantage over alternatives: they have much more information on the users of their apps. Also, because ratings are based on real names, they'll have a much easier time preventing ratings spam.
Because of this, Facebook has the potential to develop a more accurate app recommendation engine and solve the problem of app discovery. If Facebook can make their platform more merit-based than the capricious Apple App Store, both users and developers will flock to them.
And this isn't even considering Facebook's social graph. Not only could Facebook recommend apps based on your demographics + interests, it could also recommend them to you based on how much you previously liked the games that some of your OTHER friends liked. Things like this could add a whole new dimension to app discovery - all completely exclusive to the Facebook platform.