the sc2 custom map thing is pretty big these days. they have a whole 'arcade' section of the game designed around customisation, you should try it out :)
The brilliance of WC3 was the named-game system that allowed people to host whatever and fill games instantly. Battle.net was much more social-friendly too, and the editor itself provided a lot of power, but was not insanely difficult to figure out. I found the custom games in SC2 were of quite low quality just because of how much work it took to do anything.