I definitely get that, because I can see how the very qualities about I like are things that make it seem bland to others. Events play out so quickly that it kind of feels like a recap meant to get the viewer up to speed in preparation for something else, which sounds bad, but I like how none of the basic story beats you're already expecting feel over-emphasized in a way they would in any other of these movies. The scene that sticks out for me as the perfect example of this is Bucky's fall. Bucky's hanging on to a metal bar, Cap's trying to save him, oops there he goes, and all this happens in like 5 seconds. It's hard to imagine any other modern action movie not milking that for at least 10 more seconds of artificial tension. I also dig how unambiguously good of a hero Captain America is. I don't mind that the later movies tried to problematize him more, but I like that we got this one where he's just this untrammeled beacon of positivity and heroism. And I enjoy Hugo Weaving as Jordan P Red Skull.
I probably feel the way about Eternals that you do about First Avenger. I recognize that it had a distinctive style among the MCU films, and I wish it had clicked with me, but I unfortunately just found it boring as shit.