I'm so sad, that I can't play this last game of the great series due to heavy lags :(( I'm stuck at the very beginning, it's just unplayable.
I hope this will be fixed sometime (although I don't have real hope, since there's no change since 2011 (comment by thinman)...
It's a real pity... damn, this series is just great! :(
Great game 5/5! :) but it was over all too fast :(
Some tips if you get stuck:
1. It worked best for me to beat the levels one time to get to know them, a second time to earn the special challenge achievement and a third time at the 3-star(=gold leaf)-difficulty to earn the achievements for completing all levels with silver and gold leaves (and 3 times, of course).
2. Pause-Button ftw ;)
3. (Someone said that already) Begin with leveling up Crit, then Dmg and Health. After that you should aim to complete reducing costs, regenerating health and the other skills and spells.