Cavern Navigator is an easy to pick up and play game that builds more tension than one would expect. Basically you navigate your path through a cavern that scrolls from left to right by moving your finger up and down to stay within the bounds of the moving rough walled tunnel. You keep going until you bump into a wall -- then you die!
There are 3 levels of difficulty and the game can save your high scores on a remote leaderboard. The control (drag up or down) is quite responsive and the intensity grows the longer you keep moving through the cavern.
It might be a good game to pass around with a bunch of friends in order to see who has the calmest nerves and can get the highest score.
The game probably isn't for everyone since the graphics are limited and there are no specials, power-ups or other things to break up the cavern crawling, but I've enjoyed it -- plus it's hard to beat the price!