Accessible via StarCraft II's free Arcade section, "Unreal Arena" looks like a really fun way to kill some time between matches, and perhaps to practice unit control and micro a bit.
It's a classic 6v6 capture the flag game, with three maps and with some really powerful grenades. Something similar to these grenades implemented in StarCraft II could actually make waves.
StarCraft II Arcade Highlight: Unreal Arena [YouTube]
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