You acquire a Nanosuit at the beggining of the game, an advanced piece of equipment that literally makes you a super soldier, enhanced strength, sprinting and yeah... you can turn invisible.
Because of all the abilities the suit gives you, there are a lot of different ways to complete each stage of the game, wether that be facing enemies head on with super strength and fast sprint, or pacing your self for those awesome stealth kills.
Crysis 2 is a sandbox game, however it is not open world, but the level space is so big that there are countless numbers of ways to complete each objective.
The visuals of Crysis are some of the best I've ever seen on any console or PC. The explosions are epic, the scenery is so 'clean and overall the graphics are just amazing.