Single player is kind of meh in general. I found it to be little more than a shooting gallery, complete with endless waves of brain-dead enemies that seem to pour out of the cracks in the floor. One level features a construction zone with a cement tube suspended way up in the air by a crane. When I saw enemies perched up there I just started laughing.
The regenerating health bar just doesn't work for me in single player mode either, I find combat has no tension when I know that I can just hide for a few seconds to heal. There is a mode with an actual health bar, Classic mode or something, and that can be a bit of fun (I played one level with it). But I think you have to beat an easier difficulty to unlock it.
More on topic though, I hate the grenade launcher. I don't know why, but tubers tick me off much worse than Masties or Proxies. Instant death and they only need to hit near you.
CCP comes In handy In some cases. Anyways you know what I hate the most. Dead spots like not many play GG and the other selections besides TC, Heros, Conflict.