Wonderful game. Just got the 100% on hard medal. I did notice some things that could be tweaked though.
I found the game started out really hard and then actually got easier all along the way to the end. By them time I got to the end of normal I had like 50 crystals in the bank. I never had to pay cash for anything. All you have to do is make sure you are starring each level as you go. The post final boss levels are quite hard, but you can level up your gear quite high to handle them. You can also start the hard mode to level up your hero and gear and then go back to the challenge levels.
The store's items auto level to be better than what you have, which is nice. The bug here is that it only seems to auto level from gear purchased from the store. If you find / craft something, the store items stay at a lower level. If you find yourself in this situation, just buy that low level weapon from the store and go out and back in to the store and the store item levels should be at their proper level.
Gold drops as a whole are very low, but items are worth quite a lot of money to sell. Selling items is how you make enough money to buy things. The in level gold and perks to boost gold output are kind of useless.
The level up points also seem pretty useless. I put half the level up points into hero damage and the other half to hero health, and at the end of the game, I am getting 200 points damage from these level up points and 13000 from equipment.
The max mana is locked at 300 near as I can tell, so the active spells are too mana expensive to use. All I did was get L3 grenade and L3 shield to move on the passive boosts, and this worked well for the whole game.