The biggest problem is the button layout that don't always work. Escape to exit the crafting menu is not very intuitive and also might cause that you go to the menu by accident like I did once, and it doesn't seem to be possible to play full-screen without existing with the escape key, and the right click can sometimes open a option menu in the browser. Also, the learning curve is a big steep because it takes a while to learn what items do what is the crafting menu doesn't pause the game which I guess you can get used to it eventually, but it's just too hard to learn how to play while being constantly attacked. Besides, the item description isn't detailed enough, I think, it took me a minute to figure out what did what.
Overall, this is the best game I have played so far, the previously mentioned issues are just a bit too annoying, but the gameplay is solid and fun, and the use of the theme and prerequisite are really good.