If you ask me, diamonds gems crystals or whatever they are shouldnt have a limit in their chance to be found (well, the limit would be 100% actually, but you know what i mean) That is the main part of the upgrading system, so putting a limit to it so fast is kind of annoying, and for the gold, gosh man... it just takes waaaay too long for me to get enough for the next weapon, and doing some maths about it, getting a 15% or 20% more gold from the monster you were 1 hitting with the previous weapon to the one you ll be 1 hitting with the new weapon is a bit low... you could put more weapons or make them cost less gold
I liked the game but since you have all skills maxed out since 1st lvl it is a bit boring at some point, like normal atacks dont do any damage and at the begining it is difficult to recharge mana :P Other thing is that the weapon and items you get doesnt give very good stats... like, 10 def for a monster that deals 400 damage...? xD