well it was obvious that Will has been training over the last 2 years while in witness protection. he seems to be a really strong guy now. and remember that he didn't even do too bad against Allison on last years finale. however, he should have just killed her when he had the knife at her.
the tearing the ceiling down was awesome i thought. and it wasn't really the ceiling, it was one of those flourescent tube panels. and i think the tubes themselves came down too.
also, Will totally had the element of surprise. Allison got in a few hits, and then he just went at her. i don't think she was prepared. and she's proven herself to be extremely arrogant, so she wouldn't have anticipated Will fighting back successfully.
i think it was slightly far-fetched though. i would have liked it better if Sydney had come running down the hall kicked Allison around a bit then Will grabbed the knife and stabbed her. but it was so unbelievable that it was unenjoyable. i didn't even think for one second about the unlikelyhood of such a thing until an hour or so after the episode. it was just such an emotional, heart pounding situation. so i think it was real enough. and worked really well. but i don't think Allison is dead.