Thanks so much for the bug report. I definitely want to add diagonal attacking before the game is finished, I might even add it to the next version, but there won't be sprites to represent diagonal facing for a while unfortunately.
The Slime boss actually has a hard shell that reduces all damage by 90%, when he breaks apart you can attack the "core" for more damage. The fight is a little lame right now, I want to add a few moves to him like jumping and trying to crush the character, and maybe an ero attack or two.
As of the last update you can actually right click to block, but a dodge option might be nice down the line too, as dive rolling in close combat doesn't always work.
Thanks again for the list though, I'll add the things I wasn't aware of to my fix list.