Pros: * This is a good start for a game in the style of classic vertical shooters. It's still a fun game style to play. * Controls are pretty good, though a little floaty (it feels like you drift a little) but maybe that's intentional? * Holding space bar fires continuously is greatly appreciated! (I don't want to accelerate an onset of Carpal Tunnel Syndrome with games where I have to constantly jam on the buttons to fire over and over again.) * Starts easy and difficulty scales up nicely. * Some variety in enemy formations is good for mixing up the action and keeping players on their toes.
Cons: * Despite the different enemy types and movement formations, the action can be a little repetitive. Are you going for something like Geometry Wars where the action just keeps getting more intense without a break? If not, maybe consider putting in a short break with "Wave 1", "Wave 2", etc. to give the player a quick moment to regroup and also feel like they're making progress. * Will there be power-ups or some other feature that will give the player a little more in terms of strategic options for how they play? That would also help provide a little more variety and less repetition. * Some additional polish items (small bursts when enemies are defeated, rather than just disappearing), impact FX & sounds when your ship's bullets hit targets, etc. will go a long way to make the moment-to-moment gameplay more satisfying.
What's here is already pretty good, though. Nice work!