Why it's difficult: All-out battles without the use of stealth can be pretty challenging, even on Normal difficulty.
For the most part, Crysis can be a fairly tough experience but not a frustrating one for many players as long as they use the capabilities of the suit. However, the difficulty of this game absolutely skyrockets if players opt for the highest level of challenge possible.
Enemies in Crysis become more aggressive and smart while trying to shoot the player into smithereens, which will happen quite often. A player's reflexes need to be perfect if they wish to get through Crysis' massive levels with such elite opposition.