Oh noes! Teh Locust are in ur planet, sinkin' ur citiez! Ha! Seriously though, Marcus Fenix and his fellow Cogs have seen better days. The lightmass bomb from Gears of War ended up doing bupkiss and now the Locust are working to sink Jacinto, humanity's last stronghold against the subterranean invaders. It's enough to make a man want to cry. Well, cry on your own time soldier, as there are Locust hordes to slaughter, and a whole bunch of achievements to get to boot.
The good news is that most of the achievements are very doable with only 40 points from public multiplayer matches. That's not to say that work isn't involved in getting these achievements, but compared to the original Gears of War, these achievements are a walk in the park. A war torn, Locust infested park, but a park nonetheless. Spoilers abound, so you've been warned.