I'm not talking about serving in the armed forces or law enforcement, but rather a simulated role-playing environment that strives to replicate the main aspects of an FPS.
While there are plenty of games that have the mechanics of an FPS in real life (i.e. laser tag, paintball), an FPS simulation with character and universe immersion is a newly realised concept. The first one was created just this year, and is going through its maiden run in Melbourne, Australia.
IRL Shooter
This was a project run by a bunch of independent film industry guys seeing if they could put essentially combine laser tag and role playing. When the notion was first introduced, the gist of what we were promised was an immersive experience with real actors, real props in a detailed environment. The guns were laser technology but were supposed to have real recoil and sounds (sadly the latter part was stymied by Australian customs and our gun laws).
In short there are naturally teething problems and technical issues to be expected when running an unprecedented project built from scratch, but what one gets is an immersive experience which gives back as much as you put into it. Get into character and in this incarnation you're a soldier enlisted into a private security firm employed by a sinister corporate conglomeration which is trying to regain control of a research facility that has suffered an outbreak of a zombie virus. You've gotta infiltrate the facility with your team of six and find out what the hell happened, and whether anybody's alive... or whether the whole place has turned into a grotesque zoo of zombies and monsters.
Despite the shortcomings with the weapons (which ended up having crappy sound and no recoil), the experience was nonetheless very satisfying, with creepy atmosphere, mystery and intrigue and conflicting reports and a slightly open-ended backstory. For the average person who's never played paintball let alone been to a combat zone this was a good test of teamwork, reflexes and fitness... and funnily enough there was a lot of interest from members of the armed forces who were itching to test their skills on a recreational basis. I was kinda halfway in between, having plenty of paintball and FPS experience, compared to my teammates who had virtually none and screamed every time a zombie came charging out (and I mean charging). So they pretty much all agreed that I should be field commander and I got to draw upon my tactical simulator experience (thank my many hours playing Rainbow Six) and managed just about every action my team made until we were a smooth efficient unit. Even if the game itself wasn't particularly challenging for a veteran, I still felt a real sense of achievement that we all defeated the boss, completed the mission and made it out with no casualties, and that indicated that it was a good experience.
In fact I was so excited about this project that I even made t-shirts for my team. We're all resident doctors, so...

Haha geddit?
At any rate, to be entirely honest, being the way I am, if I wanted to feel the real visceral thrill of risking one's life and limb (and face), where I could pretty much go all out, I would still prefer paintball. But paintball doesn't have this kind of roleplaying experience which encourages one to get in character, and is physically demanding and caters to a much smaller audience (i.e. none of my friends, because they're wimps).
When the whole process is refined, and perhaps when some of the other obstacles have been overcome, I would recommend this "IRL shooter" experience to any who have caught themselves wishing they could saddle up and be the ****** they're playing as in their FPS.