¡You responded me! Man, i feel like my head is going to blow.
But first, i think i need to urgently react about what you said about the AI.
You may think your game does not have a good AI (lie) but an example you can't say "that is not good" is the indie game called "12 is better than 6"
if the enemy sees you, you are [swear word of your choose] and while all of the guns have a slow bullet velocity (for the standards of wild-west ammunitions) if you get just a little overwhelmed or make a little mistake, you are dead.
¿Not enough? No problem. Intravenous, another 2D game, has a pretty similar example with the difference that if just one and one enemy sees you, then go making a hole in the cemetary because you are sovereignly FUCKED. Just a little tiny 9x19 mm Parabellum SubSonic (less than 340 meters per second) can let you with 1 little percentage of your total life and keep in mind, most of guards have sub-machine guns, assault rifles and shotguns.
If you feel that is not enough then take a look to enemy's reactions:
If they hear shots, they'll go to the place of the sounds and start lurking for you.
If the see blood traces, they will follow them till the found the dead body.
If they see a corpse (alive or dead) they will try to wake him up (efortless when they are dead) and start looking for you.
If the lights start to flicker, they'll pay attention for a couple of seconds and then proceed.
If they lights are turned off (with the buttons or the fuse box), they will try to turn them on again.
Assuming that you think that's not enough, then take a look at your game. If a merc sees you, he will alert his buddies and take cover, getting out only if you lean over it or if you are tu much time behind it. It doesn't stop there if the electric monsters (i do not remember their names) see you, they will start WALKING towards you. If you don't attack with your firearms, they will know that you are planning to use your knife so when they are close to you, they'll suddenly sprint and (in most cases) cath you off guard. Not like is easy to attack them with a knife without being hurt anyway but it's quite interesting.
Letting the AI topic apart let's talk about the games you took inspiration from:
Stalker: I could see that one coming and what a message it leaves...
Metro: I'am not so sure about what metro you say (2033, Last Light, Exoddus) but if there is a thing that i'am well aware is that i love metro, and knowing that, i may start liking a bit more the 3D project. Knowing that you took some inspiration about it. Will there be sections where you can shoot lights so they can't see you? Maybe ocassions where you can pardon their lives and leave your enemy's unconscious (i wouldn't because they are just a bunch of assholes... the mercs)?
You aren't discarding the 2D project? That's great to hear!
You may feel a little mad because of the long reply so i'll put a little bit of an interesting thing about your country (it was poland. Right?)
The Blyskawica submachine gun was the World-War-2 version of the Scorpion Evo 3 (at least for the standards of the firearms at that time). It was a polish mass-produced, cheap and reliable pice of gear and boy if i see even a newborn baby with this, i would poop my boxers and start begging for my help. My god if it was even easy to produce because of the using of screws. It was like taking the best things of an MP40 and a STEN jointed together.
I'am not so surprised about Poland making very good weapones. Take a look at the PM-63 for example. What a system of fire and what a portability. I bet that Harry Houdini could hide a PM-63 in it's throat.
Best of the PM-63 is that even on it's 9x19 parabellum version, it is still subsonic. Can this get better?
(i apologize if i overwhelmed you with the message)