Tidalis

Tidalis is a block-based puzzle game with casual appeal, hardcore depth, and an addictive new "streams" mechanic. The game is brimming over with riffs and variants on that core mechanic with 20 game modes, dozens of special blocks and items, and 115 levels in the adventure mode alone. The basic rules of the game are this: blocks fall down into the board and have a color and an arrow direction. If a stack of blocks exceeds the height of the board, you lose. In order to clear blocks, you must right-click and drag paths through the arrows to set up chain reactions of like-colored blocks. If this sounds simple, that's because it is -- you'll be lining up lengthy chains within minutes. But you'll be surprised how much brainpower it takes to set up combos of multiple chains, and the many brainteaser-style puzzles include some real stumpers.