So, I've played through the first hour or so of Prototype - here's are a couple of snap judgements.
Controls are a bit weak, hopefully I get used to them. You're basically holding RT the entire time to sprint (AKA run over/through everything), which is fine - except someone decided to also bind the airdash to RT(while you're in the air). So if you're running from roof to roof, you'll jump over short gaps, hold RT to sprint across the roof EXCEPT WHOOPS YOU HADN'T LANDED YET AND YOU AIRDASHED AND FELL 6 STORIES.
Graphics are nice, runs smooth. Exactly what you expect. Some of the "Web of Intrigue" cut scenes have real actors, which is a bit odd and jarring, but nothing that really removes you from the experience.
Missions so far have been generic "let's get you familiar with the controls" type stuff. I definitely sense potential for tricky stuff, different approaches, etc. Using the disguise mechanic works well, and functions as expected.
Quite a few "holy shit" moments, at one point I was being chased by a "strike team" (Prototypes apparent version of the GTA cop swarm). The helicopter carrying them popped up on my mini map, so I grabbed a taxi, ran up the side of a building, and chucked it at the copter, exploding spectacularly, then crashing onto the soldiers that had begun zip lining down to the street. Very slick.
There appears to be a a time trial based event system in the game, where you have to accomplish tasks in a set amount of time. So far this has just been climbing up a building, and running across rooftops. You gain experience based on how fast you complete, and I assume there are achievements based on getting the top scores. Annoying so far, but hopefully easier once I'm familiar with the controls.
Expect a full review once I finish, so far it's about what I expected: a sandbox title with a seemingly lackluster story, but very slick presentation.