Wait, how is this movie like TLJ? I really hope that's not the case, as that is probably the most disappointing movie I've ever seen. Would put a huge warning flag if this movie is compared to that shit.
It turns out that when Luke disappears at the end of TLJ, he was actually traveling over into the Marvel universe. But then he dies in this movie too.
I'm not saying no jokes are allowed or anything like that but the Endgame trailers (especially the first two or so) had a very dark tone. Now, I didn't expect the movie to stick to that tone for 3 hours (this isn't a David Fincher movie) but I was expecting something a little more grim than we are used to. It sounds like Infinity War is probably darker overall than this one, which I was not expecting.
I think last impressions mean a lot. I've seen plenty of people here characterize Infinity War as 2.5 hours of nonstop action even though that's literally true, but can feel like it since the last 30-40 minutes is a pretty big battle (and the beginning 30 or so mins has a lot of action too). Infinity War has a lot of humor in it, but the movie also ends on probably the biggest bummer note I've ever seen out of a mainstream Hollywood blockbuster, so your first thought coming out of it is "shit, that was really dark." When half the cast suddenly dies, your first reaction isn't going to be "hey, that movie was a lot funnier than I expected."
I think the opposite might be true of Endgame. If the movie ends on a triumphant note (pure speculation here: I'm going to guess this movie doesn't end with Thanos killing the other half the universe and now everything is perma-fucked), I can see that last note of triumph overriding whatever melancholy feelings take precedence in the first hour or two hours or whatever.