Insurgency is one hell of a beast, created by mixing up all the good things from other great FPS title.
It has the realism of Red Orchestra / Rising Storm that adds a great immersion and intense atmosphere, the small skimrish maps akin to Counter Strike for a quick and fun close quarter battles, great weapon customization system that reminds me to Rainbow Six / Ghost Recon, and Battlefield's class based gameplay.
Looks unoriginal eh? Nah, not at all. Insurgency DO feels like a combination, something "in between" of those game, but the devs executed the ideas impressively that I can consider Insurgency as an original, somewhat one of a kind game that still maintain its own unique identity among an ocean of FPSes nowadays.
Immersive, intense, hardcore, yet it still can offer a fun and enjoyable experience. Insurgency is one of those "easy to learn hard to master" game. Naturally, Insurgency itself is a very simple game, the thing that you'll have to learn is how the general system works, weapons and attachments, the different set of classes, and the realism factor itself. I believe you'll fully understand how the game works in around an hour, or even less. Insurgency isn't for a trigger-happy FPS player. Patience, teamwork, and careful observation of your surrounding is the key here. Even if you already do that, like walking slowly, crouch, peeking on corners, you'll find yourself in "WHERE THE ♥♥♥♥ IS THE BULLET COME FROM?" situation, first shot, screen blurred, second shot, you started to panic, third shot and you're dead. In many occassion you don't even have the time to be panicked, you'll have an instant death.
Another great aspect of this game is how devs design the overall system. No grinding, no perk, just pure skill and tactic. ♥♥♥♥load of varied game modes that actually..well..varied, a balanced class system. Overall Insurgency is, one of the most balanced and fair FPS I've ever played.
I could've put it in the gameplay section, since the sound isn't just to make the game more atmospheric, but the sound design is a part of the gameplay, its a crucial part. For a modern military FPS with a flare of relism, the sound must be designed to make the game, not only immersive and realitic, but also "usable" and its actually a part of the tactic. Yes, the sound is mind-blowingly fantastic. I love how detailed the sounds are, the sound of bullets blazing over your head, hitting the wall or floor, fly near your ears, and when it do hit you, everything become muffed. The guns sounds realistic, it doesn't sound too weak, yet doesn't sound THAT powerful. Sound is your best friend and your greatest enemy.
Insurgency is built from Source Engine, which is, in a way..dated. But. thanks for the great level design and visual effect, and of course the gameplay. You'll find Insurgency's graphic to be a brilliant one. You might think Battlefield has the most realistic graphic for a FPS game. That might be true, but Battlefield's graphic is just too beautiful to be realistc, I find it more in the cinematic side. Insurgency, in the other side can capture the overall atmosphere of a battlefield. A battlefield is supposed to be "ugly", no filtering, no lens flare, it's rough. No, no.. I don't say Insurgency graphic is ugly, far from it. It's a bit dated yes, but the "dated" factor and the genius devs behind the game make Insurgency's graphic looks truly believable.
Immersive, believeable, realistic, hardcore, tactical, yet still fun, enjoyable, and pretty much accesible. Insurgency is a perfect balance of realistc / hardcore FPS game with the close quarter combat fun and quick matches of a more arcade-ish FPS game. Insurgency does take inspiration from a wide range of FPS game type, but the devs cleverly managed to distinguish the game to something more unique that can stand at its own two feet and overall maintaining its own identity of a new kind of FPS game.