This is a really fun game with a few issues, but none of them are game breaking. The leveling seems to be glitchy. The stat increases are completely random. I've had as much as 150 points to distribute after leveling and as little as -80 points after leveling. I don't know if that's by design or not. Also, sometimes the stats I've already spent will change.
I like that on the character window it shows your basic stats and a compiled list of all your item bonuses, but it would be really nice if it also showed your derived stats from your stat distribution (for example, show me what my crit chance and crit bonus is from the points i have in agility).
Speaking of stats, they are really uneven. Agility is far superior to strength even if you're using a melee weapon. Also, some item combos are fairly easy to get for how absurdly powerful they are. Playing as the rock star using the ghost bow, ring, and amulet I didn't even have to try on nightmare. I just now started on hell, but I really don't think hell will be able to challenge this combo either.
Basically, if you want a challenge in this game you have to challenge yourself by ignoring superior builds and playing around with other options to see if you can still clear the game.