This game is easy to learn, but incredibly difficult to perfect. The upgrading of the bikes can be tedious, but I finished upgrading the 9 main bikes over a year ago, and still enjoy playing this game every day.
If you must binge play a game, don't play Trials. If you are like me, and can play a bit and then continue with your life, I highly recommend it.
A couple tips:
1. Be patient - upgrades can take multiple days to finish, and you can run out of fuel quick.
2. Don't use diamonds for anything but fuel tank upgrades. Want to use diamonds to speed up an upgrade? See #1.
3. It is possible to beat the game and unlock all tracks without spending a dime. That being said, I recommend spending a couple bucks to get rid of ads.
4. Play the slot machine often - it has some great prizes and they get better as it levels up.
5. (This is the most important) Add some friends! Racing against other people's ghosts is always more exciting, and much more challenging. I can't tell you how many shortcuts and speed techniques I've discovered by racing other players.
I love Trials because of how easy it is to learn the controls, but how difficult it is to master them. I'm constantly learning how to overcome different obstacles and improve my score.
With the addition of the Bunker, the Donkey, Agent, Stallion and now KTM bikes there's always new content to keep things interesting. I look forward to what they add next.