Got back from the movie a while ago. Absolutely loved it. I had already spoiled myself reading the synopses and was pretty upset about what they did with Cap, but watching the movie, it totally makes sense. I guess I was expecting an Infinity War Part II in the sense of there not being much in the way of character development, but that's largely what the film focused on, and made it pretty clear that Steve hadn't actually moved on from Peggy, and vice-versa for Ms. Carter herself.
It also helps that I think it's heavily implied that Cap didn't retroactively retcon Carter's family, but actually made a seperate timeline to live out a life with her. He didn't go in with his shield (which was busted anyway), and the shield he had when he returned was clearly a different one, one that looks...I don't know, a bit more modern maybe? It gives off a more higher-tech vibe.
Little disappointed that Captain Marvel kinda just fucked off for the whole film, I was hoping that perhaps she'd have an active role (maybe forming an army to fight Thanos...but that was prior to me knowing they'd just kill present Thanos right off the bat). Also kinda annoyed that for all the talk of having an arc for Bruce Banner and the Hulk over the course of Ragnarok through Endgame, to see that he just figured it all out no problem off-screen was pretty frustrating. But I think in those cases it's simply an issue of greater priorities The movie is three hours as is, and those potential subplots, while potentially nice, aren't really necessary for the film as a whole to feel complete and satisfying.
I also feel having a past Thanos being a villain kinda dampens things a bit, since I think it'd be more satisfying with present Thanos, who instead gets killed feeling victorious. They even lampshade the fact that Scarlet Witch is getting revenge on a Thanos that hadn't done what she's getting vengeance for and didn't even have any idea who she was. Nevertheless, they make it work, and the film's strengths overpower those minor nitpicks that I can just shrug it off.
I think the time travel explanation doesn't make a lot of sense, though, and that still kind of bothers me. The Ancient One states something about the Infinity Stones needing to be all present in the universe to keep it stable or something to that effect? That could work as a narrative cop-out... except the main timeline doesn't have any Infinity Stones now, so what does that say about the stability of the main timeline? Even then, those timelines aren't gonna merge back, because the Avengers seriously fucked things in at least two of them. Cap already knows to start looking for Bucky and Loki disappeared with the Space Stone somewhere in the NY timeline, so that timeline's totally off-kilter now, and the Morag timeline now has no Gamora, no Nebula, and Thanos and his army are completely gone, so who even knows where that timeline is going, but it's definitely not going back to normal now.
And bringing the stones back to the Asgard and 70s timeline probably didn't change too much, but it's just gonna put them on the path to Thanos inevitably anyway, right? It's the same situation with the NY timeline if Loki running off doesn't fuck with things too much, but who knows. In any case, are those timelines gonna have a similar run in with Thanos? Then they go back in time to undo things, take the stones and split more timelines... I just gotta imagine there had to be a cleaner time travel solution somewhere.