A bunch of enemies suddenly came out of nowhere and destroyed me. 

Fun! 

Post-process effects like bloom would be a nice touch that elevates the graphics. I would change the graphics of the ships to feed into the bloom by having light borders instead of dark ones. Think tron. I would have bright particles for explosions, along with a shockwave effect when ships detonate -- with a nice juicy sound. You might consider screen shake for when the enemies explode near you; may or may not improve the juice of the game. The UI font is terrible, hard to read nor does it do anything to set the atmosphere of the game. It looks far too comical.

Shield mechanic should make the enemies flee, I literally had it on for too long and drove them off of the screen. Had to spend a lot of time dodging projectiles for them to finally appear back on the screen. This just wasn't fun. It is also too powerful the way it is, in that if just tanks all those hits and can be used to destroy enemy ships when they come to close. The shield needs a cooldown or some kind of limit where the gets depleted and then needs to be recharged over time, maybe via collectibles -- energy that is picked up from ships that have been destroyed.

The AI needs to be improved, in that all it does is charge at you when you are shooting and then flee once a shield is on. Lastly, shooting doesn't feel good, it lacks juice. You need better sound effects and probably particle effects to make it clear how impactful they are. I also think that the player shoots are too slow; maybe these get upgraded to being faster, but I was never presented with the option as those appear randomly. My feeling is that their base speed is too slow, they should be quicker than enemy bullets with the enemy ones slower so as to be easier to dodge.

For the visual part, I’m not an artist either but I concur with what Solo Man Games said below, UI needs some work especially with the fonts (too many of them) and a bit more contrast could help. Also a point that could be nice to give the different ships more identity is giving them slightly different shapes to match their skills/stats and not just a color swap.

Now, as to general gameplay feedback, the shield mechanic is a bit unclear at first as nothing tells you it is there and also why does it make the enemies run away? Also with it having no cooldown or limit, you can abuse it by spamming right click and destroying every bullets that come close. I feel like it should be reworked with either an energy bar that refills overtime and gets consumed when used or as a proper active skill with a cooldown (press shield, get protection for 1-2s so you can get out of a tight situation).

Also, an addition of a cooldown timer or animation on the active skills would be nice.

The later waves felt a bit too long with just too many enemies, having some new enemies even if it’s just slightly bigger variants of the basic ones with a bit more health and firepower (kinda similar to the mini-bosses right now) would make it a bit more interesting than having to go through 150 of the basic enemies. On the opposite, mini-bosses and bosses waves are too short and the enemies there could use some slightly more complex AIs than just rushing into you (and a bit more health so they aren’t cleared in 5 secs).

Now for the two extra ships:

Military one’s gameplay didn’t really match its description & military theme. You’d expect a raw firepower ship, yet its gameplay is focused around placing bombs and luring the enemy into them. I liked playing with the bombs but it’d be more fitting for a small & quick rogue ship imo. As to the bomb upgrades, they felt a bit lackluster (notably the cooldown & detonation time upgrades didn’t felt like they had much impact) and when the game loop lasts only 10 waves you want each upgrade to bring a big improvement as you won’t get a lot of them in a run. Now, for the other upgrades, not only the Arc spread is actually a downgrade as you want aim else you won’t hit enemies, but it also does nothing if you pick it before the extra bullets upgrade. I’d rather merge them into a single upgrade and with extra tiers so you can get 5 and maybe even 7 bullets at once, to get that raw firepower feel (to counterbalance the spread with number of bullets). Also the bombs’ damages are a bit too op as you can one shot the bosses with them.

The religious ship felt like it had too many things put in it with its 3 active skills. It also wasn’t clear that the Sacrifice Wave & Ordeal skills were one-use only (I was waiting for their cooldown until I got them again in the upgrades). Both are quite op though, so if they weren’t one-time use they’d need some nerf. The crusade daggers felt good overall. Throwing them is a bit weak and near useless, or you’d need significantly more daggers as, due to the spread and lack of aiming you’re not guaranteed even one of them will hit unless you’re truly close to enemies. But if you’re close-range, you’re better off directly running into the enemies with them, which is an effective though high risk strategy. However, there was a bit of the same issue as to the military’s bombs with the further upgrades as in they don’t hold that much impact (ie. +1 sword? that doesn’t have a big impact when you start from 8).