Ran into a few bugs, the red enemy bullets seem to collide with my own bullets so spamming at them would block their attacks, the cylinder bomb seems to always float up to the top right when dropped, pressing the 'S4' button on UI doesn't seem to do anything. Also not sure if it is a bug, but you can hold 'E' and drag the gravity field thing around wherever you want, this is actually cool if its a bug I would suggest trying to make it a feature :D Also the UI seemed to not scale to full screen.
I did have a fun time with the skills though! They could use some more feedback so I know what is happening, and I can't tell if they are on a cooldown or use mana of some kind, having that displayed on the UI would be helpful too. The gravity well, and rewind time ones are especially cool. I would have preferred being able to hold down the mouse button to shoot though, clicking a ton of times isn't ideal. You could try shooting while the button is held down, and have a reload time or something after X amount of shots or something like that.
I think adding some more polished UI, and better spell graphical/audio effects would go a long way!