Attack on Titan is a phenomenal show and I haven’t been this excited about an anime in a while. Aside from live action Evangelion Pacific Rim.
Anyway, the basic premise is that 100 years before the show takes place a bunch of rampaging naked humanoid creatures (Titans!) suddenly appeared and killed most of humanity. The remaining humans created a settlement with 3 huge walls to keep the Titans out.
There are 3 walls: Wall Maria, Wall Rose and Wall Sina. Wall Maria is the outermost wall where the main characters Eren Jaeger, Mikasa Ackerman and Armin Arlert live. As you can expect, the poorer people live on the outermost walls, while the wealthier people live deep within the walls.
After 100 years of peace, two 60 meter high Titans appear and breach Wall Maria and start massacring people. Eren, Mikasa and Armin are caught in the disaster and Mikasa and Eren witness their mother being eaten by a Titan and are taken away by a ranger. Years later, the trio enlists in the military in order to fight the Titans.
I think the story is simple, yet fascinating. Giants are attacking and eating people for no reason, or are they? It mixes sudden dark humor, glorious action sequences (3D Maneuver Gear is so awesome! It’s like medieval Spider-Man!) and emotionally crippling backstories. As the plot advances, you see subtle hints that things that seem meaningless at first have a significant impact on the progression of the story.
All in all, it’s a show that you definitely need to keep up with. You can watch it on either Crunchyroll or Hulu. The manga is a bit further along, so if you want to get ahead you should read it. The show is planned for 25 episodes and an OVA.