He may be a tool, but he's our tool. Sure, he's a snob, a mama's boy, and a lousy politician, but he's still the protagonist. In fact, some people think these qualities are what make Coriolanus great. Sure, he's harsh—he also refuses to compromise his values, never accepts mediocrity, rejects phony politics, and always says what's on his mind.
Er, on the other hand, we could argue that these qualities are what bring about his downfall. After all, if he'd only kept his mouth shut about hating the plebeians, he'd have been leading Rome instead of planning to storm it.