Here is my take on this question:

First of all, you need great controls. You want to make sure that the player will learn the controls quickly and when playing the game, the player forgets that they are holding a controller. Movement and turning cannot feel awkward. Otherwise, figuring out the controls throughout the game can break the immersion. While this may be optional, it would help the movement immersion if the camera "jumps" up and down slightly like in Mirrors Edge if you look closely. In addition, it would be helpful if you can vault over low waist cover. Make sure the camera tilts to the side like in Medal of Honor, Warfighter and Mirors Edge. Call of Duty may allow players to do this but the camera simply floats up and lowers the weapon down off screen. Despite the differences in looks between games, this mechanic can greatly help traversing the environment as well as showing that the character you play as can actually jump like we can in real life.


Another factor is the weapon held in the hand. In the past, the weapon would just simply be lowered to show at the person is moving but nowadays, the weapon would be tilting left or right if strafing and it would "jump" up and down when moving forward. When sprinting, the weapon is not aimed at the reticule, but is lowered instead. This can show the illusion that you are playing this character instead of being a camera.



We also have the melee attack. While this is mostly best done for third person games like assasins creed and DMC, melee can also help the immersion if the animations is done correctly. The knife animation can be a simple swipe but may not help enough if the player can't stab the enemy in the game (I am looking at you MW 1). But it doesn't have to be just knives, if the First Person game has swords or axes, have different animations of various slashes like Dishonored and Dead Island. Do a horizontal and vertical slash animation. Case in point, do what the 3rd person games do; have different animations for melee attacks instead of a simple blade swipe. It's very important if the first person game focuses on melee weapons more than guns.



Recently, a YouTube e channel called smosh games released a video talking about what makes a good FPS game and somewhere, it has more on that melee attack thing I mentioned earlier. Check it out if you need some ideas what makes the genre immersive.

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Good, intuitive controls.

Seeing some feedback of the character (in BF3, vaulting over things. In mirror's Edge, waving your arms and the screen blurring/controller shaking as you fall further)

Decision making, either on rails (where you have to shoot your commander in Battlefield 3) or one where it affects the outcome of the game.

Having characters that you feel attached to always helps. This is a hard art to master, in my opinion, as it sometimes even varies game to game within a series.

Multiple options and plans of attack. Not like Call of Duty where you basically are guided through a decorated maze (even Battlefield does this, as much as I love it). Borderlands is awesome in this regard because it gives me an objective to accomplish and obstacles. I can snipe from the cliffs, ramp in with a car, run in and run out, or go in guns blazing. Dishonored did something similar, and while I enjoyed it, it felt more like "look at how many options you have" than actually having an open world and options.

Weapon customization is a nice one. I think it would be awesome if there was a system for modifying guns as far as attachments, bullet size, and even fine tuned things like gas ejection systems so you could fine tune your gun's performance to your specific likings. Of course, if I converted a 5.56 to a 5.45, ammo would be harder to cone by in most cases, and the parts to even do such a thing would be pretty hard to come by. All sights would have to work with whatever rails were on the gun (or else you would have to find a rail system to add to it if the platform supports it), suppressors would have to have the right threading, etc.

Also, melee shouldn't feel like I'm swinging my arm with a magic stick of death. There should be weight and resistance, and instead of swinging your weapon and holstering it every time you click, a more in depth melee mechanic (even a system of hand to hand and weapon fighting) would be a nice thing to see if implemented well.

Strong story and the sound plays very important role

Audio.

The most immersive FPS game I can remember playing was System Shock 2, and I think the biggest part of that was the absolutely fantastic audio in the game.

And what about the story dude?

I wrote something in my journal/database (evernote) on what I enjoyed about FPSs while working on my RPG concept. Yes it sounds off topic but that is because of what is offered in my concept for that RPG lol..

ToG:DoaNF is the RPG equivalent of an FPS. The instant sense of skill felt when taking out an enemy with your hand eye coordination in an FPS is unique if not rare across all genres. I want to be able to recreate that feeling within a RPG by making the player feel more involved in the commands issued as opposed to setting a command and watching it play out.

There are many reason a FPS can pull me in. It all depends on what content/aspect within that game I am taking into account.

- In multiplayer (PvP not CoOp), functionality/intuitive design of the controls is among the top things I look for.

- In CoOp I focus on the use of the space within the screen and how effective their pairing of a HUD or split of the screen is played out.

- In single player campaign I am more critical of the aesthetics (graphics, sounds, music) as well as how well the story progresses (flow, not so much the quality of the story).

But ya, like I tried to say in the quote without the rpg fluff: The instant sense of skill felt when taking out an enemy with your hand eye coordination in a FPS is unique if not rare across all genres. There are very few genres which give nearly as much of that instant sense of reward for your dexterity,reflexes and hand-eye cordination. Ultimately this is what immerses me in a FPS.

Gameplay. I can generally look past a sub par story or graphics if the controls are solid and fun to use. Bulletstorm is a good example. Im not a big fan of the whole tongue and cheek writing and story, the game was so fun to play It kept me coming back.