However, it gets a lot of hate as a weapon, whether being banned in private/ladder matches, to being abused in game for using a "noob" weapon. Here's my counter argument to why it's both fair and necessary to the health of the game.
C4 camping is, I admit, pretty lame. But is it any lamer or more powerful than any other form of camping? A sniper and bow camper have a ton of ammo and can repeatedly kill people from half the map away. With C4 you get 1 kill and you're done - if you're lucky. There's no Scavenger perk in Crysis so no more C4 until your next death.
Frustrating? Yes. Game winning? Hardly. Even then it's significantly weaker tactically than the XPAC or Swarmer, which can used in a similar fashion with no delay, 3 shots each, and no damage to the user in proximity. You have to be in proximity with C4, so although it has more power than a grenade, there's no cross map kills and unless you're camping with it (which I don't, I use it as a limited range grenade) you have to be in danger to use it, and I repeat - if you're just camping with it, you're not posting a score that even threatens the top 6.
In terms of the role it plays in balance, that's simple. It's an anti-squad weapon. In every game, there needs to be a counter to every strategy. In Crysis 3, the single most dominating strategy is squad rushing. C4 counters that. You're in a building, you see the radar, you have 3 dots rushing through the door, what are you supposed to do? Stand and fight a 3v1? Run away? Screw that - trap the door and punish them for it.
C4 punishes rushers. C4 punishes tight squads. Both are the dominant forces in Crysis 3, so it's only healthy that there's a counter for such play, and it's pretty churslish to ban it or complain as a result. I'm a rusher and if I get killed by C4, I shrug it off as an occupational hazard, respawn, then move on.