Like the game itself, let's not waste time on introductions at the start and get straight to the action. You are well aware of the franchise, you have expectations from each title. After the failure of the lightmass bomb at the very end of the first game, the Locust are fighting back in greater numbers, and there is no time to waste.
This game sheds diffused light on the origin of the locusts. It doesn't have an exposition scene describing their past but rather you slowly discover more about them through the gameplay as you progress deeper into their lair. Your objective is to bring the fight to them. No bomb, no gimmick, all-out war.
I forgive you for not remembering Carmine from the first game (who was shot in the head from behind cover by a sniper) but his younger brother is here enlisting for the COG army. The game starts off with you, Marcus Fenix, teaching young and inexperienced Carmine the trades of war by going through the basics. As he eagerly learns and becomes a part of Delta squad you cannot help but appreciate and eventually grow fond of his presence and constantly strive to get better in shooting and killing "grubs". Your brother-in-arms Dom Santiago is back, worn out by his missing wife Maria whom he is searching for desperately, everywhere he goes. Old pals Baird and Cole do not have interesting and investing personal stories here, they are merely the firepower you need to fend off the hordes of hunters desperate to sink huge cities underground to take control over the surface.
As you make your way deep into the underground caverns to fight off the Locust, you learn how the miners of emulsion are developing signs of a strange illness called rustlung which is proving to be fatal for most. You also learn the monsters are taking people as prisoners to torture them for whatever reasons. Eventually, you will make your way to New Hope, a medical facility run by the shady Dr Niles Samson where you will encounter the early stages of Locust monsters, called Scions and eventually learn the whereabouts of the headquarters for the Locust, near Mt. Kedar, a place called Nexus. Once inside, you learn of how the monsters are sinking the cities, and how some of them are getting mutated by exposure to the emulsion, and turning into "Lambent", Locust-like but capable of exploding and doing greater damage. Soon enough, Queen Myrah appears and you learn about the civil war that is underway between the locust and the lambent, and decide to kill both of them by doing exactly what the Locust were doing - sink the last human settlement of Jacinto.
Aside from the main story is the undertone of desperation from Dom who is searching for his wife from among the prisoners and it is this arc that will endear this game to you. Amidst a gruesome and gory war for the upper hand, is a story of a man and his wife who simply wants to be reunited with the one person who brought peace to him in a time of crisis. The flip side of this is the story of Carmine who is a bubble of energy trying to fit into a world too hardcore for his tender soul. The combination of these two, side by side with the steady tone of forceful mobilization into enemy territory makes for one of the most consistent experiences in a shooter you will find. The mechanics are pretty much the same as the first game so you will settle right in while the addition of more guns and vehicular combat (in some of the most exciting sequences you will find in this genre) will provide adequate freshness to a tried and tested system. There is not much to critique in a game that is learning to perfect the art of cover shooters by providing engrossing story elements and exciting sequences to freshen up the experience, but a cliffhanger of an ending does mar the joy of playing through the campaign and not reach a satisfying ending, even after a monologue in the end from the "narrator" that could not have been more precise.