Diablo is pretty boring, though I'm playing it with my friends anyway.
Starcraft belongs on any list of the best games ever made, and everyone who calls themselves a gamer should at least play through the single player of it, even if they don't like the competitive scene. Starcraft 2 is awesome too, but it lacks the atmosphere and charm of the first one.
That said, I still ever so slightly prefer Civilization to Starcraft, I think. It's very close though and really, if you haven't played both you're missing out.