I picked up SC2 in a bargain bin once, largely because I enjoyed the first one so much. I hated it; the gameplay mechanics are dumbed down enormously and the graphics actually look worse, because the units look like cartoons. I played it for a few hours before shelving it and reinstalling the original (and Forged Alliance)

The original SC, and FA, is simply the best RTS I've ever played. I still play it occasionally on skirmish, with modded AI's that are pretty hard to beat.