I have fond memories of Warcraft 3 custom maps. Some of them were very fun minigames, and multiple standalone games were based on them. For example DOTA, and Tower Defense. I don't know if tower defense was invented by the custom maps, but Warcraft 3 greatly popularized them, without doubt.
So Blizzard made a big fuss about their editor being very good. I don't own Starcraft 2 and won't purchase it. Can you point me to any outstanding Starcraft 2 custom maps ? I mean anything at least as good as DOTA or Tower Defense, that will probably spawn another row of standalone games. If you point me to some I'll watch youtube videos.