I am a big bejewled fan, and I love similar games. Trism bring that idea to a whole new level.
Instead of having block, or sqaures, or jewels, trism simply has colored triangles. The trick is, however, you can move a row of colored triangle any direction (along a row). You can move a row to try to get three matching colors together - if you don't, the row "snaps back" to the starting position. The rows wrap around, so if a triangle goes off the screen on one side, it reappears on the other side of the screen.
The other twist with trism is that the blocks will fall based on how you rotate the iPhone. As you rotate, the block will always fall down - with "down" being indicated in the lower right corner (and if it changes, a grey arrows appears briefly showing the new direction - see my last picture). So as you are deciding how to move blocks, you ALSO need to decide how to hold the iPhone to achieve the best success. Hold it one way, and you will end up with empty triangles (making it more difficult), but if you had rotated it, something might have fallen into the empty spot.
You also have poweup and other special features that you can unlock as you play. To date, I have only unlocked a few of them, so I can't tell you what they all are. There are three game modes, but I have only played "infinism". "Terminism" and "Syllogism" ar the other two modes. I know one of them is timed, but I am not sure about the other.
I give this game 4.5 out of 5 stars for it's unique gameplay and new take on an old game. The only problem with the game is the gameplay is sometimes not as responsive as I would like. It sometimes take a few taps for the game to "figure out" what row I want to move (or the game thinks I am trying to pause).