I am basically a total noob non-gamer with slow reflex. I am not a good playtester to tell you about new features as I am not really the target gamers of your game. You may want to take my feedback with a grain of salt. It's just that only money and different weapons make it feel like yet-another-space-shooter. Ok, here you go…

I could not play at the level to experience any special weapons. Maybe you have already implemented these... To make your game stand out, I think the weapons should be able to do things beyond just causing more damage or requiring longer cooldown times. Maybe some projectiles could fly around in loopy directions, unique patterns, and not just straight lines? Or, allow the player to lock on to a specific type of enemy and it will chase the enemy automatically after being fired? And maybe some fired projectiles could spawn bullets or have a blast zone, either at random timing or upon the player's key press, to help cause more damage?

And, maybe instead of money, it's some specialty weapons you can pick up after destroying a certain enemy? The player can use the newly picked-up weapon immediately to get out of a tight situation. Any accumulated unused picked-up weapons can then be traded for upgrades later. This way, the player can use the picked-up weapons as either instant or delayed gratification; it would be the player's decision. Players will enjoy the game more if they feel more empowered and in control. But money is delayed gratification only. If I can't live through the wave, money is meaningless to me.

The reason I don't play shooter games because as someone with slow reflex, I can hardly pass the first round, and then everything restarts all over. I forever get stuck at the beginning. In order for me to want to play a space shooter game, I want an abundance of shelters or shields to get me out of tight situations so I can continue -- to see all the cool stuff the developer has prepared for the game. I also want to be able to clear all the enemies within a distance in one blast, which, again, can get me out of a tight situation. Perhaps you could add a no-fail "zero-skill" level that allows players to practice everything without a game over. A total noob like me can just keep playing it with occasional venturing out to the actual level. The game can keep a tab on how many times I would have died, but I could just continue, regardless, to experience all your cool stuff you have implemented in your game. So my motivation could be trying to break my own records to have the least would-have-been-game-over as possible. Yep, it may sound pathetic. :D  Experienced shooter game players could use this as a tutorial or practice at the beginning.

I agree with the other comments that the flying objects are too small. I don't know if there are any non-enemy objects, but I just tried to shoot everything in sight.

I like the way of using the mouse to aim, as keyboard controls will greatly reduce my already-slow reflex. I would like to see unique visuals of the enemies, and flashy particle effects and sound effects of different enemies. Even if I know I won't be able to beat them, at least I'll have something entertaining to see and hear.