Planet 51 is one of the better games that have come directly from movie to PS3. The game itself is quite easy to get the hang of, with driving around and exploring being the main sources of excitement in the beginning. However, the massive game space (and lack of a map) make Planet 51 quite tough to get into. Activities like mowing lawns and parking cars are only fun for so long (and sometimes you have to do this more than ten times).
The cutscenes which are littered throughout the game are a little bit unconvincing. Although I have not seen the movie, it reminds me of games from the early 2000's where the mouth is going but nothing is coming out (or Kung Fu movies that have been dubbed into English).
On the upside, the majority of the trophies are very easy to get, I was able to get 100% in less than a week!