In my opinion, Split Personalities is absolutely topping! It's fast, furious and extremely enjoyable.
The basic idea, as Domark says, is very simple. Remember the strange little hand-held puzzles which preceded the Rubik's cube? Yes? You know, where you have to slide tiny plastic blocks left, right, up and down in order to make up a fragmented picture. Well, this is the basis for the game. You pull the pieces of pictures from the top left hand corner of the screen, and shuffle them around.
Movement is a bit tricky, because everything moves so fast, it's tough to get to grips with the cursor.