I can safely say that I will not be purchasing 2010, 'cause 2009 was the most repetitious game I've ever played.
I am willing to give it a try. I agree that once you reached the top of career mode you fought the same few fighters countless times. I think that what they need to do to prevent this is allow the player to switch weight classes like Fight Night allows you.
It was THQ's first go at the game and of course it has much room for improvement. I am hoping that they build a lot from the original game.