I think this is a really great game. It's an awesome concept and it's really quite fun for the first few levels.
The only negative thing I can say is: it gets too difficult too fast. Once you get to a certain point in the game, it's near impossible to progress without playing previous maps over and over and over again. And that can be very frustrating. I feel the same goes for the original GemCraft (at the first "Epic Level").
And comparing this game with Episode One, this is definitely much more difficult, and slightly more fun. But mana seems to fill up much more slowly here... just an observation which might relate to the increased difficulty.
Anyway, the gameplay is great. I like the whole idea of the stat points and skills, and the combining gems thing is a cool concept. I really enjoy it.