Setting. Like mentioned above, the setting is hardly original. You've got the sinister military and the infected to fight, all of it set in a present day New York, an open world where you can cause random destruction and killing. Woo-hoo.
Graphics are not impressive. Although the world is huge, the detail and texture look rather shabby. Special effects are not spectacular either. The in-game menu is unnecessarily confusing and it basically forces you to poke around.
Sound. The soundtrack is non-existent. You'd half expect something more atmospheric, given the setting and zombie-mutants. Despite the high degree of strong language the voicing is handled poorly. Alex Mercer, the protagonist, sounds spaced out and irrelevantly quiet which doesn't help you get immersed in the game's atmosphere.
Gameplay. Gameplay is good ol' rinse&repeat. All major missions are basically locating something or someone and capturing/destroying it. In the process you have to unlock your memories which allows you to find the main bad guy. There is little variety among the enemies and most fights, except for boss ones, are piece of cake. And there comes the ugly part: boss fights are ridiculously unbalanced, which coupled with poor controls, becomes annoyingly tough. It's really ridiculous. You could solo the entire strike team in a matter of minutes, but boss fights would take up ten times more time. You have an access to a wide range of abilities including stealth, though truth to be told, you'll hardly need more than 3 for casual fights. There are challenges too, as well as collectibles, but there is overall little incentive to do that.
Plot is underdeveloped. This game offers no new approach towards the classical fabula and even more so, plot is even blander and more incoherent than average. There is no immersion and connection with character, events or villains. Most missions feel rather stand-alone rather than progressing further. Prototype tries hard to masquerade this set of cliche as something more by adopting reversed narration (you're kinda reviewing events in retrospective) and that cool unlock-a-memory mission system, but it ultimately fails as game lacks the very atmosphere of mystery. In the end I didn't find the protagonist to be sympathetic or even likable, or somehow provoking me to memorize the game.
All in all, it was a waste of my time. Games like this are one-timers: you play them once, then you forget them.