I just had a bug as a Golem Explorer... I killed the boss on a level and was on my way to the hole in the floor, then the game seemed to stop and my character stopped moving. I thought my browser crashed or something. Then my health started to drop gradually but very fast (though there was no enemy) and I tried to heal but it dropped so fast I died. After that the screen went black and it still is :p.
Besides that its a great game that keeps you entertained for a while but it does get boring after 2-3 attempts.
I voted 5/5 before the bug since I do think its a good game.
Here is some fedback:
Maybe you could make it so that when you equip a certain spell twice or more you get a powered up version of that spell. Like Heal lvl 2 if you equip it twice.
I could do without a save button.
And some builds/combinations/tactics or whatever make you invincible and you will be able to keep playing forever. Which is pretty boring. So maybe you could make it harder or change some classes.
After what seemed like 1000 trys I beat lvl 58 with Lightning - BFG - Energy Homing Missile.
Use BFG and lightning whenever they are charged, and the missiles while you wait for that. Lvl 59 and 60 are easy compared to 58.