I really love the look of it, maybe adding 8-bit sounds to it (I tuned on music myself in the background to enjoy your game even more :D) and a fixed raster on which everything moves would give it a good old school feel. I definitely enjoyed it anyways, my high-score is about 300.

It's really good if this is your first jam, simple, but REALLY GOOD.

Fun game, but it was really difficult. Couldn't really get a score better than 93. Maybe add more lives or slower enemies and better collision? Overall, for your first jam, this is good.

Fun game! 

For your first crack at a bigger project this games pretty good, and the concept had me interested immediately!  Real quick before I go into in depth feedback, you should really add the concept in the description, cause it had me interested as soon as I read it.  Plus ya know, a screenshot can't hurt.

Onto feedback:

• As I said the base concept is pretty interesting by itself, the only thing I think it's missing is some sort of variety.  Maybe something to force the player to move, or some sort of different magics/enemies and combos for them? 
• The shooting feels just a bit slow, sometimes when an enemy was super close to me and I launched a... "orb" it would not reach it before it hit me, possibly delay from when I hit it or something?  I'm not quite sure.  You could possibly decrease the damage hitbox of the enemies to give the player a little leeway in how soon they actually die from the enemies.
• For movement it's kinda the same thing, it feels a little slow and since moving lead to a slower score I generally just stood in one spot defending.  Part of why I suggested adding something to force the player to move.  I feel like it would mix up gameplay, though I'm not sure exactly what, always up to interpretation.
• Just to end off, some sort of "progression" however repetitive it could be might help keep people engaged.  Possibly some sort of room system with waves you're trying to get through? (Kinda more of a wide suggestion I just came up with) It gives the player a simple goal and a "timer" to that goal so they can focus on it.

Just a final thing, there is a slight bug I noticed with the score system.  It seems that when you die the slow down applied to the score from movement isn't reset.  So you end up stacking up how slow your score is the longer you play.  It resets when you restart the game though which was useful when I wanted to keep playing.