The single-player campaign in Crysis was great, I loved it.
The multiplayer utterly sucked. Crytek screwed up one of the fundamental tenets of multiplayer gaming - NEVER TRUST THE FUCKING CLIENT.
Crytek did stupid shit like offload physics calculations to clients (which is why some matches were "DX10-only"), and also have clients do damage calculations.
e.g. if the client said "I fired a pistol bullet and it did 99999999 damage before resists" - well, you'd have an instakill pistol. (This could be achieved by editing an XML). Similarly, armor resists were calculated ON THE CLIENT TAKING DAMAGE - so if you had a vehicle with 99% resistance to all damage types, you were effectively invincible.
My multiplayer experience in Crysis was something like:
1 week of playing legitimately - constantly getting my ass kicked by obvious cheaters
1 week of trying to see what level of cheating I could get away with without people accusing me of cheating - it was shocking how far I could go in this regard (50% damage boosts to everything, no assault rifle bullet spread, 1000 horsepower pickup trucks, AA cannons that could depress their turrets by 30 degrees) without getting noticed because of the attention blatant cheaters received. Even with this, it was only a matter of time in every single game before a blatant cheater would instapistol their way to an attack helicopter with 99% resistance to all damage types and amped-up missile damage.
After that I quit.