Great first title. Gameplay uses a couple of tried and tested mechanics. Best way of getting use to game development.
There are a couple of pointers that I'd add but as it's your first, take them with a pinch of salt.
- There is a lack of difficulty curve. Enemies instantly kill the player giving no time to get use to the mechanics. This can be very off putting to a new player. Perhaps introduce a slower, weaker enemy first.
- The camera feels too close for how fast the enemies move. If you still want some enemies to spring up on you, perhaps a line of sight/lighting mechanic would work better.
- Moving from mouse to enter in a twin stick shooter can really break the games flow. Try using a key or even multiple key options that can be used while your fingers rest on WASD. Same goes for any control setup, nobody wants to do finger gymnastics. Unless your game is QWOP of course xD
Altogether, a well put together first game. Look forward to seeing what you make next!