UPDATE: Click to the comment section to see the full trailer. Updated the title since Metal appears to just have his own episode separate from the main game.
Just revealed on Gamespots “On the Spot” was that owners of both Sonic 4 episodes (on the same system I believe) will get “lock-on” technology where you will be able to play as Metal Sonic! Plus, purchasing both episodes gives you four exclusive levels. Along with this news, the release date have been revealed for the US. May 15th for PSN, May 16th for LIVE, later May for PC, June for Android and July for Windows Mobile. Also, expect to see a new trailer with a new level revealed later today.