Here's an unpopular prediction...
Valanciunus will get pushed around because of his small frame. There will be those on this board that will complain about his defense and say that he doesn't get enough offensive rebounds. Some will complain that he was over-rated, and is at best a career back-up centre.
Valanciunas will put on 10-20 pounds, show flashes of improvement, and there will be calls to trade him for draft picks (a la Ed Davis this year).
Valanciunas will start to develop into a good centre and calls for MVP will start, even though he won't be even close to it.
The moral of the story is that he's not going to come in and turn the team around on his own. He's going to be smaller than other NBA centres, raw and will need time to get bigger and used to the speed of the NBA game.