Sure, Trixel for iPhone is merely a puzzle game. And yes, iPhone has plenty of those. However, Trixel is also rarified in that it seems simple enough to be forgettable, but after an hour of play you'll look up, realize you've missed your stop... and likely opt for the round trip back just so you can keep playing.

Trixel's frightfully basic premise has you tap-flipping square tiles to show one of two colors of each side. Clustered in rows and columns, your goal is to match a predetermined pattern displayed in the upper left corner of the screen.

Child's play, but there's a catch. You can only flip tiles directly adjacent to the last one you flipped, as indicated by a throbbing cursor and up to 4 arrows describing your next potential flip-tap (save for the beginning of a round, where the cursor is placed for you)

Thus, in order to flip a tile on, say, one side of a 5-row cluster from the other, you must move the cursor one title at a time to get over there, and each move will invert each tile whether you want it to or not. It makes for a wild mix of solo tic-tac-toe, minesweeper, chess with just the King, labyrinth, and painting yourself into a corner gameplay.

Matching the pattern in as few moves as possible - even though that might involve tapping one tile over and back multiple times in order to access neighboring tiles - nets you a "gold" ranking. Silver and bronze are awarded for solving the puzzle pattern with more moves than technically necessary, and nothing is awarded for taking way too many moves to get it done. You're free to fret each puzzle for as long as you like, but you need to earn a medal to unlock the next.

Right there you've enough brain-teasing distraction to get you through the daily commute, maybe even the odd opportunity to miss your stop, so engrossed are you in the tap-flip mayhem of it all. But wait, there's more.

Later levels introduce "crystals" appearing on select, usually contrary tiles. Collecting these allows you to save up for a do-over, or a one-time move to a non-adjacent tile. Wormholes appear allowing/forcing you to jump to an otherwise no-go tile in the cluster, inverting both the departure and the arrival tile in the process, or you'll be forced to contend with bombs that blow a batch of tiles over, wholesale. Sometime you're given a cursor for kitty-corner movements, and so on.

Such cerebral tomfoolery adds depth to Trixel's already puzzling nature without forgoing the simple tile-swap premise. To wit, you'll never be at a loss figuring out how to play Trixel, only sweating the details of how to play it best.

Trixel may not carry the same transcendent weight of, say, Tetris, but considering the number of 99 cent junk Apps for iPhone, Trixel has the rare distinction of offering you all your money's worth - and quite a bit more.