That wasn't too bad at all. Add some music, sound effects, and more levels (with some other ships with special attacks/features).

The mothership was a bit to easy to kill because it spawned all attack ships from same point. You might make the attack ships spawn from a few different places on the motherhip and even spawn different types of attack ships as levels progress.

I think the game area could be bigger, by moving camera view out some. The playing field seems a bit small. There doesn't seem to be enough time to react when the enemy ships come into view.

Add a time delay at beginning of game(level) that flashes "Get Ready" or something, so the player has a few seconds to get his concentration together.

I hate those slow bastard ships that rotate and shoot, which is a good thing.

Pretty fun stuff. You could actually take GameDev back 20 years with some improvements.

Dude, awesome work.

Excellent first game on 3DGS,
Congratulations,
Loco