Amazing local co-op
Singleplayer- The game goes along a storyline which acts a squeal to the first game (which I did not play much of). You get to fight a militant 3rd party acting in Mexico as the squad leader of a Ghost Recon team. The missions are structured, with obvious objectives marked on a map, so it is linear (although throughout a cityscape much of the time, rather than enclosed hallways, which never occurs). There are some neat features, like enemies being marked once they come into sight, and then staying marked until they are out of sight for a bit. You get to control an AI squad of your choice. Each squadmate has a class (rifleman, grenadier, an AR type deal, marksman, or medic) which defines the gear they get, so a grenadier will most likely carry a rifle with an under-slung grenade launcher.
Co-op: Local (or online I guess) cooperative multiplayer is probably the best aspect of this game. The multiplayer has a few different aspects from singleplyer: first person view is forced, scope are aimed down instantly, and motion from breathing is not included. The coop mode involves the players engaging AI enemies in many scenarios.
Game Modes: There is a standard firefight setup, where the AI actively tries to destroy the players, the goal is to destroy the AI team. There is also a mode which pins the players against an attack helicopter (this can be combined with firefight). Objective based missions are also available, in which the players will fight though enemies to perform certain tasks, like planting explosives.
Notes on realism: Ghost Recon (original) was a very realistic game, where even some rebels could take out your squad very quickly if given the chance. To say this game of the same series is realistic in the same degree is debatable. Combat AI is not the most realistic (as they will act fast, still 2 players could take on 40 AI). This seems to be made for more people than the original (common tactic of formally Red Storm games by Ubisoft), although it is a great game nonetheless.