I have some small suggestions for you:
1. The collisionrange of the first big boss should be a bit smaller, i had lost by only standing right near the boss and without direct contact.
2. The mouse button should be over the menugraphics.
3. The upgrade screen is choosable
, you can click on it, the other level informations are visible too, when you move your mouse over the level buttons.
4. The character moves very stange on the title screen, you can hover over the edge of the tileset, and the movement is a bit slippy. Also there is a glitch when hitting the left side of the screen, the character begins to shiver.
By the way, nice gameplay, graphics and music