I managed to play Prototype for an hour today on my lunch break and I personally think it's fantastic. I've pretty much played all the games (At least all the ones we have in stock) for 360 and there's never really been many where i've said "I'm definately going to buy that" after 1 lunch break.
I didn't do much in the way of missions, I was having too much fun gliding over the city, jumping from great heights, killing 325 innocent people, transforming into them by kneeing their heads off, slamming their heads into the ground and just curb-stomping them.
I loved running up buildings, jumping off and gliding to the next. Or grabbing a person, or car, running up to the top of a sky scraper and chucking it off, following it down just to see what destruction it had caused.
I know i'm going to love this game from start to finish, it feels like it can only get better (once i've got my powers upgraded) So I choose to ignore IGN and say it's a definately a must buy.