I found a site www.sc2mapster.com that has custom maps recreating Starcraft using the Starcraft 2 map editor. So far the Terran and Zerg campaign is finished and they’re working on the Protoss.
I’m only a few missions in the Terrans, but so far it’s pretty cool and quite a bit harder. For example the 4th(?) mission has you protecting a base awaiting Mengsk to come rescue you. In Starcraft with mission was quite boring as you’d be attacked by a group of 3-5 Zerg every couple minutes. In this version you get attacked by 10 or so. Good stuff.