SnK only ever starts fleshing out their MCs 2/3rds in and I think characters are the most vital part of a story.
The world is largely uninteresting, due to the fact alot of its properties are unrealistic in a tedious sense. How do you even manage an empire that covers whole Africa, Europe and parts of Asia? For a series that introduces global politics as a major theme it lacks alot of political intrigue that comes with it. Where are the scattered nations in Africa creeping up on Marley? Where are the civil wars of non-Marleyan natives? Of course, we don't get to know any of that because Isayama is trying finish the series soon. Don't get me wrong, I know that Marley has been busy fighting on many fronts and has its own shortcomings, but the fact that absolutely noone but a clan from Not-Japan tried to ally with Eldians after about 100 years of isolation and non-aggression against the world is ridiculous. The hatred for Eldians also seems very contrived. Why would nations 1-2 continents away care about what Eldians did, more specifically, what they last did 100 years ago?
I could go on about this, but I hope I made my point clear. For a political shift, the manga is too simple to execute it in an amusing manner. Not enough political figures who act through pragmatism, unrealistic imperial borders and no ethnic undertones that isn't Marley or Eldian. The lack of complexity demotes this series to a shounen-tier manga.
The lore seems like your average cutout mythology. Nothing really interesting to it.
Even the fight scenes are a bore, it's just flesh mechas punching and tackling eachother until one of the survey corps members comes in to assist them.
And I haven't even begun talking about exposition scenes, the manga really likes to throw flashbacks to add up mystery and thrill, which in turn could have been wait in cleverer, more subtle ways.
If I want to read a shonen with fun battles, I read FMAB. If I want politics, I'd read novels and non ficition