Your interaction with each level isn't just limited to changing colors or falling off cliffs, either. You're not always the only inhabitant of the mazes; some of the other creatures, such as a happy-looking square blob named Stan, are helpful if you know how to direct them. Others, like the hungry Mercoids, live only to tear you apart. And then there are all the other hazards and devices, including teleporters, jets of air, objects that change your blob's consistency, dangerous drops from one platform to another and pistons and hammers that can send you flying off the track.
All this stuff combines to make one fiendishly complicated - but still maddeningly compelling - action-puzzle game. When it ships on Aug. 22, Mercury Meltdown will also pack in a multiplayer mode (which was disabled in our unfinished version) and a handful of unlockable "party games" like races and blob-painting challenges. What we've played so far is fun, so assuming Mercury Meltdown can pack in enough levels to keep things entertaining for a long time, this could be one to take wherever your PSP goes.