I'm currently trying to defeat level 30 boss. First levels are easy, but later it gets a bit more difficult. Some matches create special jewels, and you have to think when is the best moment to use them.
So far, I liked the ice block levels, and Boosters are quite helpful when you seem stuck.
To say something bad, I would like to receive more gold for completing each level.
In short, the game gets more interesting after the tutorial. Boss level (at least the 2 I've seen) are quite challenging!