Blood honestly doesn't fit in crysis, the nanosuit protects you...
I actually have blood off in the multiplayer, i just think it is in the way. If there is to much blood it will just be fun in the beginning, in the end you'd be tired of it and stop playing/turn it off. However, if there is blood in the singleplayer, it would be acceptable as long as it is on HUMAN enemies without nanosuits. Aliens may have their own type of blood, not necessarily red... (I have played games saying they are realistic, usually they include so much blood it doesn't matter what happens around you, because the blood is a red version of a flashbang.)