Chain Reaction is simply a remake of Xixit with the same engine, but new graphics (by Dana Dominiak, the president of publisher Webfoot) and music. The buttons at the bottom right seem to indicate that mouse support was planned, but that was never implemented. Since playing a Tetris-style game with the mouse was never a good idea, this is one feature that won't be missed.
Just like Xixit, Chain Reaction has several block sets to choose from. Unfortunately, only the default one is really playable, since the blocks are clearly distinguished by shape, the colors alone are insufficient, since they are too similar. Just one more example that design is not about how it looks, but how well it works.
Its similarities to Tetris notwithstanding, Chain Reaction is a lot of fun and very addicting. The game looks great, plays great, and even sounds good. Best of all, given the option to play random levels, the number of levels is virtually infinite. Great 'plasma' animations and incredible soundtrack by Webfoot musician Ariel Gross round off this fun underdog you'll spend a lot more time than you'd care to admit ;) Highly recommended!