The first trailer for Petroglyph's Mytheon gives us a bit more of an understanding as to what's actually going on in the online action roleplaying strategy hybrid.
Petroglyph shaves a little of the fuzz off of the original Mytheon announcement, which spent more time talking about microtransaction-based game that was creating an entire new genre rather than going into actual detail on the gameplay. From what we see here, you collect (or perhaps purchase) Power Stones, summon creatures, and use special powers based on the colour stones the creatures have an affinity to. It actually sounds sort of like an action collectible card game with stone discs instead of cards.
Mytheon is currently scheduled for a 1st quarter 2010 PC release.