Starting November 14, you’ll have free access to the original Wings of Liberty single-player campaign and every Co-op Commander, and will be able to unlock access to StarCraft II’s competitive multiplayer content for free.
In other words, you can now play all of StarCraft II’s multiplayer, every Co-op Commander, and the entire first campaign in the single-player story, for free.
Hmm tempting, only played the first one, might try this out now.
Source: http://www.indiegamebundles.com/starcraft-2-goes-free-play/