Entertaining single player, great multiplayer, and pretty graphics all make Burnout: Paradise worth investing in.
The open-ended gameplay is a refreshing new direction for the genre, and Paradise pulls it off beautifully. There is simply an unending amount of stuff to do, and even old challenges get harder as you progress. Hence this game gets a replayability rating of 9.0, same as its overall rating.
The graphics are great, the gameplay is smooth and interesting, but the real magic in Paradise city comes out in the cars. Intricately designed and widely varying, the numerous cars in the game are just simply beautiful. Add to the coolness that they each have different functions (you'll see what I mean when you play it), and you actually have some strategy to do before you enter another event. Pick x car, go to y stoplight, start it and then go find that sweet stunt spot.
There are motorbikes as well, but I find these less interesting.
The multiplayer in Paradise is a rush, especially with all the times constantly being updated. Since it is a couple of years old now, fewer players are likely to appear, but you'll still get a good challenge out of racing whoever is online.
Paradise takes the cake for best racer of 2009, and is in my classics collection. Play it and see just how fun it is.