This is unrelated to the current conversation, but I think I've managed to articulate the major things that bug me about AoT.
Undermining of expectations, basically. When I started, I thought I was getting into a Humanity, Fuck Yeah sort of story. For lack of a better word, there's an aesthetic to humans fighting against something so much larger than themselves, and with the Titan-shifting thing becoming so integral to the plot, it's looking like that's going to fall by the wayside in favor of ever-more powerful supermonsters. I had kind of expected that whatever Eren's dad did was going to result in super-soldieriness - Titan-style regeneration, sure. Maybe some super strength or enhanced reflexes. That's actually what I thought was going on with those sequences where time slows down, like when he uses Annie's leg-kicking move against Jean, or when child Mikasa stabbed that dude or present-Mikasa dodged that Titan's attack when she thought Eren was dead during the battle of Trost. I mention that because I had also kind of thought that Mikasa had a similar deal going, with different strengths, a significantly cooler head, and more self-control and experience, which would hopefully allow her to remain a major character without getting overshadowed by Eren in this hypothetical.*
There's that, and this Titan-shifting thing and, in particular, the way the Annie-Titan keeps demonstrating new abilities apparently pulled out of her metaphorical ass whenever it's most convenient for foiling the protagonists. Increasing power as the series progresses isn't a problem, in itself. I mean, I liked Gurren Lagann, and you don't get power ramp much more blatant than that. It's just that when it's done casually as a way of negating any progress that's happened so far, it starts to grate. We don't really need so many episodes demonstrating Grave New Threats in this. The Attack on Trost arc did a fine job of providing motivation, and a Titan with human-level intelligence (doesn't have to actually be a human, even) is a perfectly adequate way of escalating without overdoing it. There was already the implication of it with the wall-breakers, so it'd be a neat way of making that reveal. It just feels like all that's been accomplished is getting a bunch of vaguely interesting people killed.
Speaking of which, I'm a DM. Introducing and fleshing out interesting characters just so that you can kill them off at appropriate moments, or inappropriate ones, is a thing I can get behind. But you have to leave some of them alive! And the only ones that feel safe in that regard right now are Eren, Mikasa, Armin, and (to a lesser extent) Levi. Killing off the squad in the attack on Trost was a good move, but doing the same thing with the Scouts is repetitive and doesn't really accomplish much as far as I can tell. We're just going through the same motions again, which might be the point, but it isn't very interesting.
*I'd gotten on a bit of a tangent on this point, but I will say that one thing I like about the way things have turned out is that Mikasa's skill and strength appear to be entirely due to her own willpower and inherent badassitude, not something she got as a prototype for whatever Eren's dad was working on (which I'd suspected since it seemed implied that he'd seen her before the kidnapping-murder visit). It's a nice silver lining that she's responsible for her own awesomeness, and she's going to retain a hopefully unique place in the story.
All that said, it's a fantastic series and I haven't been gripped by anything quite as strongly in a very, very long time. I highly recommend the anime, and I should read the manga.