Like with some of the other PSP games, I purchased them because of a family member. In this case, because a member of my family loves Tetris and other puzzle type of games.
Thus, I picked it up and started playing and had a lot of fun. The depth of the game doesn't appear that great, but this is basically tetris where you line up 4 blocks and the pieces can fall down rather than creating holes. It's an interesting concept and is programmed with excellent graphics.
I would say that you should rent this to see if it's worth playing over the long haul. A lot of people play this way, but you must like the concept and like puzzle games.