Prototype looks good, but feels fake. The city is densely populated, which is great when you're upping the mayhem, but otherwise looks artificial. You're running into the same three or four models. I understand that even current gen systems have their limits, but the 360 has delivered better. Alex looks at little better, but suffers from stilted, choppy animations. However, if you're into super violent, visceral polygonal death... well, you'll like Prototype.
Even the city looks plain and repetitive. There are enough distinct landmarks in the city that you won't get lost often, unless you're on the ground. Prototype also suffers from short draw distances. Long-range combat is sometimes a pain and it adds an extra level of challenge/ frustration to orb hunts.
Sound, on the other hand, is pretty good. A considerable amount of "f-bombs" are dropped throughout the game, but the voice acting isn't all that bad. The rest of the soundfield is filled with the sounds of chaos; gunfire, screams and radio chatter.