Incredibly fun game to play!
When you first start playing, Alex won't have a lot of powers to use, but as you progress and earn evolution points, you'll be able to buy upgrades that will help you during the game. Some of the powers are the ability to glide, to turn his arm into some sort of big axe, and more.
The game plays great. Controls are simple. It simply feels "natural" to play the game.
Graphics is one of the game's weak departments. It doesn't look as great as some other recent games but its not like it looks awful.
Sound is about average. Some voice acting is plain wrong while on others are good. Sounds from guns, cars, and the people in NYC are all fine and add some sort of realism to the game.
While the game doesn't have a mutiplayer mode, it still offers some replay value. As you progress you'll unlock events. Events are some sort of side missions in which you have to achieve a certain goal within a certain time frame. While it may not sound that interesting at first, some of them are really fun to play and if you aim for gold on each event, some of them can be plain hard.
All in all, Prototype is a great game with great gameplay totally worth full price.