I like what you did with the game, I think the controls were pretty sweet and the graphics, music, and sound effects were minimalist but fitting. I especially like how the gun flips while you reload; I thought it was a nice touch.
That being said, I'm a bit more critical than some of the other commentors here. I know I'm going to sound harsh, but I'm only trying to make this game the best it can be. I know it's tough making a game in such short time, and it's even tougher to make one with 12 levels. So, in no particular order, here are some of my thoughts:
-The game's regular difficulty is way too hard; I think this might be because you have 8 bullets, the enemies take 4 to kill, and you almost always face them 2+ at a time. So any missed shot means you have to sit and reload while an angry enemy charges at you. -If you run out of bullets and ammo pickups, you're pretty much defenseless. I think there's one level where the exit locks until you defeat all the enemies? That wouldn't be very good. I feel like you should have some backup melee just in case. -On the level where you first get the key, the disappearing blocks are almost all off-screen, and the ones that aren't are obscured by the GUI. Those blocks should be front and center to show what the key does (granted, it's easy to figure this one out, but keep this in mind for future jams) -The time between game over and retrying is too long -There has to be a better way to show that you're losing maximum health when you get some bullets. Maybe shorten the health bar when you pick up ammo instead of rescaling the green portion? -Similarly, there has to be a better way to show ammo count, and for differentiating between ammo in your gun and ammo in reserve. Maybe make the active ammo bigger? And shown with bullets drawn on screen? -I hate level three. The fact that those guards can spot you as soon as the level begins is incredibly cheap.
Also, I got this error on the first level with the laser turret (version 1.02). Might be because I destroyed the turret on the same step as it shot? I know that's a common error with GameMaker.
############## FATAL ERROR in action number 1 of Step Event0 for object obj_playerArm:
Variable obj_laserTurret.ignoreRange(100008, -2147483648) not set before reading it. at gml_Object_obj_playerArm_Step_0 #############
Again, I hope I don't come off too critical here. I think you made a pretty great game here, but with a few minor tweaks, you could have had an incredible one.