Starcraft has held up amazing well. Sometimes I'll try and play the campaigns and I always end up bored with them now.
But my favorite thing still to do with Starcraft is spend a couple days putting together a really good 256x256 map. Usually with up to six players, lots of resources and lots of natural barriers. Not necessarily ones that cut a player off, but really narrow passages that force players to pass through one unit at a time.
Then I try and make everything appear as random and natural as I can. I'll make most other places with resources be on an island or raised terrain. And I'll even test the map several times before I'm satisfied with it. Just to see if the map is too open or too claustrophobic.
I hate that you can only have so many doodads, though. Cause I like to make big forrests as much as possible. And then whenever I've created a map, I'll tell my friends about it so they can play it with me but they never really get around to it.
I never could quite master creating scenarios in the map. I'd always try to create a bunch of rescueable units, but if had the map set on scenario (or whatever) then when it began, each players wouldn't have bases and the map would instantly end in defeat. And I'm sure there was a proper way to do it with the trigger and junk but I could never exactly figure it out.