Looked promising
The starting graphics looked really promising for a simple traditional top view shooter. Controls were as normal and the gameplay was on the level as expected from these type of genres.
I do question your colour scheme though. Maybe it's my eyes, but I found it really difficult to distinguish enemies at most times. I think there needs to be something to make them stand out more. Especially in world two, I was straining my eyes to see. Everything was white and blue - the floor and the enemies. Put some distinction between them. It also helps to aim. And also, in some cases, the dead enemies don't look particularly dead. What I mean to say is that when they've been killed it also needs to be more distinguished. The reason for this (and for some games having huge red splatters) is to actually help the player identify that it has been killed and move on to the next target. Here I find myself shooting corpses alot because it's hard to tell.
Going along with this is actually the choice of sound effects. It's a small thing to most people but actually I find your choice of sound effects too similar. The reloading sound and the damage sound are so close, I found myself panicking everytime I finished reloading.
Also the perks are a little weird. They are quite slow to begin with, which isn't a problem, but then you have these bonus perks that appear only a certain levels so it's hard to decide if the points should be spent or saved. There needs to be a clearer system behind the perk points. And maybe more to cover the more 'basic' perks like bonus speed and fire rate.
It's basic and it's not particularly inventive. I will say to be mindful of the overall look and presentation of the thing. Sometimes going for the more 'realistic' graphics instead of pastel colours can make things hard to distinguish. It's fine if certain enemies are 'cloaked' under this effect, but not all of them.