This game is my go to time killer, it's not for everyone though.
You should NOT buy this game IF you don't like spending hours trying to perfect a level, or use 30 minutes on a level and then have the game tell you that you took too long.
Although this game is so rewarding when you pull off that insanely difficult jump, or when you beat everyones high score. This is a time waster, if you make it through to the extreme maps, then I'd say good luck.
The difficulty of the game ranges from beginner, easy, normal, hard, extreme. When you are on the beginner maps you'll blast through the levels, although when you move up, it'll of course get harder - a lot harder.
The game has 1 big bug which could put you off buying it though. It's that low fps cause a slowmotion effect, which renders the game more or less unplayable. A solution is to lower the settings, but i'd just like to include this.
The DLC that's out so far (3 out of 6 planned) they're all worth picking up IF you like the game. I'd say they're more difficult than the other maps, but not by much. In each DLC you get atleast 9 new trails. I think you'd have to be a person that wants to get the best medal on everything to justify the 5€ price tag though.
I personally love this game when I need to take a break from everything. It's calming and frustrating in a weird sort of way.