Was really looking forward to trying this one out, and you did not disappoint. For a first game this is amazing. Controls feel precise even with the keyboard and only took me 2 tries to take out the top cat and get the cup. Graphics are spot on. You also did a great job making the bullets stand out.
Now for some constructive feedback:
I think your firing point and hitbox are a bit to the right of the sprite. Not an issue in itself, it just triggered my OCD :).
It's a shmup, it needs some kind of score for bragging rights.
Since there's no variation in shooting, and no energy limit, ammo or speed change, you could just remove the fire button and have it fire automatically, or have an auto-fire toggle button.
The music is a bit too mellow. It needs to be a bit faster and more aggressive, to match the chaos on screen.
Overall I really like it and will be following you with great interest.