If you haven't heard, the Starcraft 2 map editing suite is so powerful it allows you to create completely different game types - something akin to Little Big Planet 2. The latest user "map" is a remake of the classic side scrolling shooter Metal Slug, complete with two player co-op support. There's even vehicle support for true Metal Slug action!
To play you'll need the beta version of Starcraft 2 or the retail version, which releases on the 27th of July. The map itself is less than 20MB in size as it uses all existing Starcraft 2 assets to recreate the first Act of Metal Slug. Something like this really shows the potential of the upcoming suite of tools that Blizzard is going to provide with Starcraft 2.