Romney was strong: he showed a solid substantive grasp of policy and was more on point and articulate than he had been in most previous debates. Giuliani, who has been out of the media eye for a while and will be again after tonight, reminded a lot of people (including me) why they like him, I think, with his reasoned and grounded answers. He also had the best line of the night, quipping that Romney would have put Ronald Reagan in an attack ad for the 1986 immigration amnesty. Fred helped himself by demonstrating thoughtful-but-conservative policy stances on a number of issues, especially health care, and by showing some fire in various exchanges.
On the other hand, I think McCain may have hurt himself slightly tonight: his personal punchlines against Romney might have worked decently in previous formats but (to me) just seemed rather cheap in this more intimate setting. As for Huckabee, to steal a line from The West Wing he seemed like a .22 caliber guy in a .38 caliber world.
Of course, none of this may end up mattering very much, either next Tuesday or in the longer run.