Very entertaining! I see a ton of potential with this game. A series of chapters is great. On a critical note (as others mentioned previously) - A few more upgrade paths with the skills, and some loot, e.g., finding treasure chests or looting the mobs for that awesome piece of armor :) The game is already great, but with a few tweaks it could be 5 star material!
Great concept! Did find it a bit too easy to upgrade, or rather would have liked a few more upgrades. Does get pretty tough past level 20 though. Good job!