It's an interesting game. Starr Long, original Project Director of Ultima Online, talks about their desire to go back to first principles, imagining what an MMO could be like without the detritus of influences. No fantasy setting. No taking turns to bash monsters. At it's heart, Tabula Rasa is a third-person shooter, like Gears of War. It is, as one of the beta-testers said on the open chat channel when we were playing, "a breath of fresh air."
The biggest difference in approach is combat. Based around your character's abilities rather than your own ability to point a cursor over someone's head, Tabula Rasa's combat is more about situations than bare number-crunching.