Some random thoughts. I didn't read the comments, so I'm sure there's a lot you've already heard.
- Shouldn't switch to SMG every time I pick it up if I already have it. Just give me the ammo.
- Art style is very appealing. As long as you keep texel size consistent it will look great. Only missing link for me right now is the skybox.
- Love the details like the shells and mags you leave behind.
- Movement and shooting feel great. Very solid foundation.
- Enemies should probably hear your footsteps when you're running - you can run around behind the guys in the convience store and they won't notice. Might also give them a higher detection FOV, or modulate this stuff by a difficulty setting.
- Keeps feeling like I need a flashlight - but if you'd rather not add a flashlight for level design purposes I get it. Maybe a very dim point light that follows the player would be good to help differentiate walls when in pitch darkness. You could also make shooting generate a flash of light.
- Death sound is excessive but funny.
- Level design is good so far, I like the way things loop back around on eachother sometimes. I like the variety in encounters - larger, more open areas contrasting with the tight corridor parts. I feel Duke Nukem influence.
- Weapons are all somewhat interesting, but do still fall into the generic "standard boomer shooter" archetypes. I like things like the plasma gun's stun feature, although I'm not sure how often it would come in handy unless there's bosses.
Overall: Nice entry - I'd like to see more.