I only have stadium, which i put 5 hours in to and paid 1k for it.
From that, I would say it is worth it. There are some premade maps you can play on, but because of the nature of the game they are short but take a lot of practice to get a perfect time on. They take between 10 seconds and 3 minutes each and often times if you want to get a medal (need certain amount to unlock next set of tracks) youll have to replay maps a few times
there are also servers which can have 50 players all racing on the same map at same time (collision is off) and you compete against them to get a good time. servers use custom tracks.
i havent tried the level editor at all
if you want, pretty sure they have demos, which let you play the game for free for 2 days (only have unlocked the first set of tracks and no multiplayer)
07-Oct-2014 07:59:37