What really annoys me about Eren is how slow he is to take things in. It feels like he's the most childish of the bunch, which really started back in season 1 when they all figured out who Annie was and Eren was like "No I can't believe it until she kills maybe another 10 soldiers, then maybe I'll think about it" and he has that dumb look kn his face of "NO WAY!!" When everyone else had long took grasp of the situation and are showing more realistic emotions like fear, being puzzled and maybe even betreyal.
This happened this season with the R&B reveal as well. If they didn't show a lengthy scene of the survey corps preparing for the possibility that R&B are also outsiders/titans, I could have stomached the scene that followed. But even after Reiner straight up shows Eren his healing power and tells it to him straight, Eren is still having this stupid look of ":O" while Mikasa again goes straight down to business.
The more I think about the last episode too, the more I dislike it (Eren's part in particular). The whole set up of that titan that ate his mother showing up there with Hannes around felt...artificial? Is that the right word? The author needed a scenario to awaken Eren's new power in a dramatic way and just kinda lumped it all in there with everything else. It disrupted the flow of the events around them, where I was focused on the scouts vs the titans and Ymir's situation in the midst of it, suddenly we're pushed back to remembering and reliving Erens emotions from the first episode and pretty much freezing everything else while they continue what felt like a separate plot in their own bubble in that battle. The whole dialogue about the scarf thing was pretty lame too, really out of place. (Armin waving his sword in the background was pretty funny too. Anyone else would have been eaten by the titan easily).
What really gets me about Eren is the fact that he's the most shounen type character in the show, and acts like one in contrast to everybody else. I don't really mind shounen characters and shows, but putting a one dimensional character togethet with others like Erwin, Reiner and Ymir is off putting and just puts the spotlights on Eren's shortcomings as a character instead of reveling in his badassry, self-loathing and beating-the-odds character. I get what people say about him being a protagonist that is set to fail despite whatever power he obtains, but it doesn't excuse how undeveloped he, and Mikasa by extension, are. Right now it feels like Eren is just being dragged along for the ride and even if that ride is just 'kill all the titans', it wouldn't hurt if he had his own agendas for a protagonist instead of being swept up in everyone else's plans. Maybe that's why he fails so much, but i digress to that point, the author could still play it well and have a good pay-off for Eren, but I really find consider him(and Mikasa to some extent, though I find her more tolerable) a blemish on an otherwise great cast.