I will make suggestions for alternatives in each case:
Dead Space 1 & 2 are fairly decent. Would probably make my top 100 but definitely not in the top 50 range. Both System Shock 2 and Resident Evil 4, which Dead Space is a merger of, are better. I would definitely say they're worth playing but aside from some aspects (for example, later zero-G sections) it's not going to take your breath away. They're close to greatness, but I would not encourage you to push through if you're not feeling it.
Vampire the Masquerade Bloodlines is a tragic game. The setting, premise, atmosphere, concept, writing is all great, but the gameplay never came to fruition. The level design is based largely around realism with almost zero consideration for gameplay and therefore not very engaging. The combat is a mess. It's also generally unfinished, as the story goes with its development issues.
The designers clearly did not have gameplay as a priority (pretty common among RPG devs, honestly) and that's a real shame. It is not comparable to the likes of Looking Glass despite what some may claim, and it is very unfortunate. Instead of VTM:B, I would recommend 90s/early 2000s Looking Glass-born FP/RPGs as well as Fallout: New Vegas.
Aliens vs Predator (2010) is mediocre. Who told you this was legendary? If I would recommend any Alien or predator game, it would be Alien Trilogy (1995), but only behind about 30 or 40 other FPS first. There's no legendary, or even great Alien game (disclaimer: not played the recent Dark Descent, which is in my wishlist).
So what horror FPS would I recommend? You can't go wrong with Blood (1997) and Quake for a horror FPS with a lighter tone and more action focus.
Dying Light is also pretty great for a modern game, though very light on the FPS part.
Doom 64 is fantastic, and was ported to PC in recent years. Doom 3 if instead of graphics innovation, the focus was on simply being a good game.
Call of Cthulhu: Dark Corners of the Earth is a cool though flawed Horror FPS Action-Adventure Survival Horror (hard to put a label on it). It's not the best thing ever but it is a gripping, impressive game with mature tone, and doesn't treat the player like a retard.
Morrowind has the potential to be one the greatest RPGs ever made...with at least three more years in development. Preferably more.
I love the game, it's the best Elder Scrolls, but I've never completed it, because the devs never completed it. It's a broken, unbalanced mess that even 100 gameplay mods cant save. Arx Fatalis, which Morrowind completely overshadowed, is the better game (though flawed itself), and if you like games like System Shock 2 and Ultima Underworld, well why haven't you already played it? It falls short of true legend status but damn does it come close.
Unreal is a solid 8/10. It's quite rough in areas though, and takes a while to pick up the pace. It wouldn't be my first pick for FPS. Unless a certain mod was installed (mine). If I could recommend only three FPS, they would be Doom, Duke Nukem 3D, and...Everspace if 6dof FPS with roguelite elements counts.
Diablo (1-2)...are autistic clickfests. I appreciate the build diversity potential but the core gameplay is pretty crap, click click click and also with level design being something obvious to point to as there isn't much to speak of (except it's quite pretty, but that isn't level design). What would I recommend instead...anything I recommend is going to be quite a lot different here, as clickers are lame.
Might come back to this later.
Mass Effect and Doom 3 were in this list, but you already told... I've forced myself to complete almost all Bioshocks which were... well, crap. Dishonored was boring as hell. Fallout 3 and 4 are boring too.
Agree with all that, though I adore New Vegas, and think Fallout 3 and 4 aren't the worst thing in the world like some will claim, they're just not great.
You are missing endless amounts of gems , and have been listening to the wrong people. The mainstream has a habit of parading around the most braindead crap as the best games. It's not uncommon to see recommendations for "all-time classics" with zero substance where there is a far superior version available, with System Shock 2 > Bioshock being one such example you can relate to. It's better in literally every way that counts.