I'm not normally one to rate anime, since everyone has their own tastes. But here's a quick look at what makes Attack on Titan unique, and see whether it's an anime for you, no spoilers included.
Story: The story can drive you nuts if you're impatient. A lot happens, and the pacing of it feels a little rushed at times, but information is vital for both the characters and the viewer. It's focuses on a very war-oriented theme, where what you don't know can and will hurt you, and that is a central theme in the story. Therefore, the story writers are very selective about which information they hand us, and when. If you're into anime for the "feel good" sensation, this might put you through an emotional wringer. Still, I really enjoy the way that the story is being told, with just enough information given for them to plan a next move. It feels like an action and a mystery at the same time. Another thing I like about this anime so far, is that every episode is full of meaningful action and information, and I never felt like I wasted my time watching a single episode.
Animation: Excepting a couple episodes that felt rushed and unfinished, the animation is definitely impressive. It shows off mostly during battles, with characters zipping and slashing their way ferociously using their gliding Maneuvering equipment.
Sound: The sound during the anime is good, though not overly impressive. Both opening songs are amazing, and really convey a sense of urgency, which carries into the episode. Vocie acting is realistic and not annoying.
Characters: Before I started watching this anime, and friend told me "not to get attached to anyone." Now I will give you the same warning. It hurts... in the heart. A lot. ;(( It makes the series very realistic in the sense of war time casualties, but it also hurts character development a little bit. Nevertheless, the characters who do stick with you throughout the series grow tremendously, and snippets of their past and history get tossed in like candy from episode to episode. Seriously, just when you start to like someone in this series... don't. Just don't. I also found the two or three main characters the most disappointing, and really enjoyed all of the others. The relationship between the two main chars is so overdone, I'm surprised they included it at all. (brother x not-blood-related sister)
Overall: Attack on Titan reminds me of several war novels that I used to read, where it invades your worldview and forces you to think about how people act given certain dire situations. Though the books, Hunger Games, weren't perfect, they also picked up on themes concerning humanity and fear. At the same time, if you didn't drop the series on your first episode, it leaves you hanging on thinking something good can still happen. On an intellectual level, I give it a thumbs up, since there are so many possibilities to speculate on. On the physical level, it's gory and horrifying, so you have to be willing to invest yourself emotionally in order to really appreciate it.
Definitely watch if you want to experience something different from the usual cutesy, or just plain lazy anime out there.