I usually don't like to write reviews on things that aren't completed, but I couldn't resist this time. I'll be honest, Attack on Titan was one of the first anime I watched, and I really liked it. But the anime is NOTHING compared to this. I expected a simple, mindless action manga, judging by what the anime offered, and the 18 volumes that are out at the moment far exceeded my expectations.
With such a large amount of characters, making readers care about each and every one of them is a difficult thing to pull off, but Isayama does it just fine. I especially liked the arc that focused on Ymir and Christa, I just thought their relationship was so nice and it gave depth to two characters that could have been completely useless. As for Eren, Mikasa, and Armin, they aren't exactly the best main characters, but they're all good in their own way, they all have their flaws and good traits alike. Oh, also, this is a bit off topic but I love that they're none of that "power of friendship" crap that's in most shounen.
**Incoming spoilers**
Now let's talk about the story. I thought that this manga wasn't going to have much story at all, aside from killing titans and making military plans. That all changed with the arc where the Survey Corps decided to overthrow the king and they started to discover more and more about the Titans. While some were upset that we didn't get to see Titans for a while, I think that part did a lot of good for the story.
If I have any complaints about Attack on Titan, it would be the pacing. Some parts are a bit too slow, some too rushed. I also didn't like the way Isayama revealed the Armored and Colossal titans' identities, it didn't feel right.
Overall, Shingeki no Kyojin is an awesome manga that I would totally recommend for lovers of action series, this was a much longer review than I had hoped, and I can't wait for volume 19.