Closest game to SC2 in terms of gameplay is almost certainly Starflight, although it's about six years older than SC2. Doesn't have quite the same lovable charm, but it does have similar 'explore a vast galaxy, find resources, upgrade ship, contact aliens'-type gameplay. Its storyline is a little less central to the game than SC2's, IIRC, but it does have one and it's reasonably interesting.
I'll have to second Planescape Torment. It's very well written, with quite an original setting.
Also, in the vein of Age of Wonders, there's Master of Magic, which AoW is heavily inspired by. You can think of it as a cross between AoW and Civilization. It also runs just fine in DOSBox.
Also, hi again everyone.