There was a map from StarCraft I called Quake Team Fortress or some other variant of Team Fortress, and you could have a team of 3 or so that could pick specialized units to fight with. It's much like some of those base maps where you have to defend your nexus, only you control you're units. It was so much fun, but no one seems to remember it to bring it back. The editors of those times are fading.
It was a capture the flag map is similar to some maps in that you start out with 1 civilian and pick a unit. As you get more kills, you get more civilians. I think it's 1 civilian per 5 kills. The first team to 30 wins. Perhaps someone can recreate it or make it all new with StarCraft II units.
I can't find any videos on it or sites other than the one below, but the map was pretty simple, you had a square high ground around your flag in the back of your base, and you had to sneak in and downstairs to get it. There were certain flaws like how the ultralisk couldn't get down stairs. The map was a facility type. If you captured the flag, you turned into a corsair with ridiculously weak hp/shield/ It was enough that one or two hits would kill you.
And mind you this was StarCraft I. You didn't change the numbers on attack rates or movement speeds.
I think ultralisks were formed because there were magical spots on the map, maybe just the center, where if you brought 2 or 3 of a unit, they'd merge into a powerful unit. Maybe 2 hydras made an ultralisk. Also the map was not really big. In fact, it was more like the smallest map. Each base only had one entrance, a main room to each base. Half of the main room was the back half where the lower ground was where in the flag was kept. And a small walkway all the way around the high ground.
Also the stairs to go down were back in the corner. I don't think we have stairs in SC2.