Squad is multiplayer, unfortunately. It's a great military sim experience with a bit more of an arcadey touch (teams have respawn tickets based on how they're doing on the missions, so dying doesn't mean you sit and wait for the operation to end). I'd suggest trying it. There aren't many games like these for single player anymore, unfortunately. Single player shooters are going the way of the dodo, I'm afraid. For a great nostalgic experience, check out "Brutal Doom". I have tons of fun with that. It's oldschool Doom 1 and 2, with physics and new weapons added and all kinds of unique new sprites for shit like blowing limbs off of imps, chainsawing shit in half, the blood effects are incredible, and it can be very challenging on higher difficulties. Loads of fun, I promise you- and it's free. The soundtrack is also fucking METAL.