Squad may still be in alpha but it's good enough already for you to consider jumping in: Evan named it in his list of best Multiplayer FPSes you probably aren't playing (opens in new tab) (and the reload animation for its M4 is one of the best in gaming (opens in new tab)). If you haven't formed your own band of brothers yet then you'll get your chance next weekend—the game is free from Thursday (November 9) at 10am PST.
It will also be half price for the whole of the weekend, which will put it at £15/$20. For that you're getting slow-paced firefights with large squads in modern, Afghanistan and Iraq-inspired maps. It's more realistic than games like Battlefield, but tries to be more accessible than Arma, which should be a happy middle ground for a lot of people.
The game is in Early Access, and will be until the end of this year. The full version will boast 50vs50 battles, base building and a full garage of vehicles.
If you're unsure whether it's for you or not, then read about Ian's time with it last year (opens in new tab). He was impressed, and the game has come on a long way since then—the developers are constantly updating animations, tweaking maps and adding new weapons.
Here's the Steam page (opens in new tab).