Whether it has co-op or not, Prototype is definitely the spiritual successor to Crackdown. Unlike Crackdown however, we were immediately struck by the movement of the character, which was highly acrobatic and felt surprisingly natural (as natural as someone running up building faces can be). And the super-powered nature of the character means that the exploration and movement aspect of the game is much more important and complex than the simple "jump good" of Crackdown. Your character, young hotshot scientist Alex Mercer, has a wide variety of powers at his disposal, usually revolving around shapeshifting and absorption. If you've ever seen the comic character Carnage, you'll have an idea of Alex's powers in-use.
The main gameplay concepts revolve around this shapeshifting and absorption, and that's also how the main story progresses. When Alex absorbs a person, he gains their memories, abilities and appearance, and therein lies much of the game's inner workings. Certain important characters will have important memories that can be viewed as cut-scenes, and their memories will add to the larger conspiracy you spend the game unraveling. The setting is New York City, and it's under siege by the military after an outbreak of an infectious biological weapon (which your powers are somehow connected to).
Your shapeshifting powers are selectable via a circle menu and range in style, effectiveness and visual fidelity. The offensive powers have a wide variety and should more than satisfy all those who want to explore the city fighting things and gaining evolution points to spend on all the different powers. You'll gain evolution points for fighting, completing objectives, advancing the story, and more. Those evolution points are then spent on character upgrades, giving Alex more powers and movement options.
The sheer movement of the character in Prototype is animated, and then subsequently combined with the power selection, in such a way that if you so choose, you don't really ever have to stop moving. You jump, flip and run in a way not unlike a combination of Ryu Hayabusa and Spiderman, and even then, you can do more than either of them. You can run right up the face of walls, you can glide like a flying squirrel, and your jumps trace a much longer arc than those in Crackdown.
While you'll definitely be moving a lot in the game, the absorption aspect is going to be integral as well. Not only will you find key story people to absorb for "video memories" but you'll also have to contend with a light stealth element as well. In short, your shapeshifting powers give you access to more character models than just Alex Mercer, allowing you a pair of forms. Alex, your default form, is unchangeable, and will always be shot at by enemies who detect him. Now, your other form is your "pocketed" form, and resembles the last person that you absorbed.
This ability to shift between two forms will play a part in the game, as we saw in-game in a military encounter on the streets of New York. Our demonstrator was losing the fight and chose to absorb one of the soldiers, stealing his form. At this point the game's complicated GTA style detection system kicks in, and despite your new form the enemies still know it's you. We saw two ways (though we were told there might be more) to take advantage of the new soldier form, one, use a specific power that confuses the enemy into thinking that another solider is Alex, two, just run away until they lose sight of you for a certain period of time.
The soldiers didn't look like much more than cannon fodder though, and the best enemies in Prototype are the ones that were noticeably absent from Crackdown. That is, those enemies with the same sorts of powers as the player character. The ones we saw, Brawlers and Hunters, didn't look remotely human and appeared to be able to match Alex move for move (though perhaps not power for power.)
With so many different facets to it, with the open-world genre being rather open this fall, and with the possibility of online co-op coming back, Prototype looks solid and entertaining, evolving the open world genre in bigger and faster ways. The only flaws evident to us were some draw-in fog way off in the distance, and the occasional clipping or texture error, but the game still has months of debug time, and things like that will hopefully be gone by the time the game ships this fall.