Well, recently I stumbled across a really nice piece of modding work which gives us fans of realistic tactical shooters a very nice option (and we all know how few of those options we've got to start with). It's a mod for Battlefield 2, and it transforms what is a pretty arcade-ish online shooter into the most teamplay-oriented tactical shooter I've ever played (and I pretty much played them all).
The gameplay reminds me heavily of Red Orchestra, in terms of seeing people take cover when under fire, work together (or die horribly) and other such immersive factors (as opposed to being grenade spammed by a bunny hopping maniac).
However, the modding team of Project Reality took realism even further - this is a nice thing when being a modder, you don't have accountants breathing down your neck and yammering about target audiences and investment risks.
To name just a few key differences from the classic online shooters widely available:
-there is no frag score scrolling on the screen. This has a severe impact on the e-peen crowd (which is good) as you don't get personal glory and gratification for taking down an opponent with a knife. Instead you get the satisfaction of moving your team that much closer to achieving their objective. It also means that you have to use the available onscreen data (i.e. seeing the guy fall down dead) in order to confirm the kill. If you don't see it happen, it may well be you getting shot in the back next.
-for infantry, there is no overhead minimap handily showing objectives and nearby friendlies/enemies (you can open a full map but it takes about a second to open up and it impairs your view). This can make it a bit confusing to start with, but you learn to stick with your squad quickly. It also has a side effect of making people communicate over VOIP a lot. You have to call out targets and threats manually, there is no handy Red Dot system to do it for you. It also means entire squads can easily slip behind enemy lines and do their thing with a total element of surprise. I was in a recon team yesterday and man, did we have fun.
-realistic ballistics and bullet damage/penetration. Don't duck behind a thin tin wall - you'll get drilled. You can also pick off enemies across half a map with a scoped rifle - snipers can pick you off pretty much from where you can't even see them.
-realistic wounds simulation. You get shot even once, chances are you're going to bleed out soon if a medic doesn't patch you up. You have a field dressing kit, but that usually just helps patch up grazing shots or minor injuries, it won't stop bleeding. Its also great for shooting up enemies - you don't have to empty a whole clip into them, if they don't have a medic handy, even a single shot will finish them off, only slower than a headshot.
-realistic vehicles. What I like the most is that vehicles are a real asset. They're extremely powerful, a single APC well used can pin down several infantry squads. However, they take an extremely long time to respawn after being destroyed, so there's no ramboing around in a tank (which you need three people to man to be at top efficiency). Losing them also costs tickets.
-heavy teamwork emphasis. As in any other online game, you do get a number of "lone wolves", usually snipers going for personal kills, but they mostly get shot up quick. Without useful information from your squad members and coordination from the squad leader (and in turn the commander), you are pretty much a sitting duck. Not to mention that six people have a much greater chance of surviving a firefight (which are usually short and brutal) than a single guy. In squad gameplay, I've seen people using real life tactics when doing urban warfare (like having a point man, base of fire, frog leaping, covering 360 degrees between squaddies and so on) and the best thing is - it works!
Being a veteran Red Orchestra player, I did find it a bit easier to get into all that extreme long range rifle fire than a usual FPS player is used to, but the level of imersiveness and the range of activities you get in PR is just amazing. From taking a boat ride to an enemy occupied city, dashing across streets and hugging walls for protection, watching with the binoculars while the squad leader lazes an enemy forward base for an air strike, taking potshots at enemies so distant all you see are silhouettes (and taking one down), tense close quarters combat where you can get dropped faster than you can say "C" in "Counterstrike", being dropped by an unsympathetic chopper pilot in the middle of an open square and cursing all the way to cover... its moments like these that, in my opinion, make a great game. Not big explosions and run-and-gun fragging.
So if you haven't tried it yet, and like tactical shooters with a heavy emphasis on realism, try this mod. I highly reccomend it.