Hexcells is a fantastic game. The puzzles are so well designed, and the presentation is so soothing you never feel irritated by lack of progress. Currently on 5-1 of Infinite and it took me hours just to get past the first couple of moves. So good when it clicked
Being the broken record that I am, I highly recommend checking out the devs other games as well, especially Sentinel. If you want to, I can dig up my impressions on that game, but the dev knows a thing or two about smart and appealing game design.
Edit: Finally page two!