I loved this movie so much. After my disappointment at watching Captain Marvel a few months ago, I'm really glad Marvel produced something like this to keep my faith at them. I would list the reasons below.
First off, there are more emotional and less generic dialogues in-between characters. Marvel's old-fashioned dialogue wasn't bad. But it feels less dramatic, and as I said, too generic. In this movie, I actually like the dialogue.
Secondly, they add more details to situations. For instance, the aftermath of Thanos is shown vividly and almost gracefully in the movie, piece by piece, which makes me really feel obliged to sympathize with the other half of the universe which survived, yet mourning every day for those who didn't.
Third, I like how they also make even strong characters feel more human and more real. Like Captain Marvel and Thor, and even Iron-Man himself, appear distressed and beaten up. Or like Hawkeye, which seems tough at heart, but even he cracked up and turn to a monster after losing what he loved.
Fourth, I like how they switch the movie from a really sad drama to dynamic fight scenes with still witty consent to emotions characters show when they do fight.
Fifth, the color selection, the cinematography, and the CGI has improved a lot since Infinity War. It carries the movie radiantly and softly. I even remember comic strips being re-created perfectly in the movie.
Sixth, there are things which appeared as a plot twist. There are characters which die unexpectedly. And there are more possibilities for future movies. You'll watch the movie yourself to understand what I'm describing. So, we're left with more excitement to watch more Marvel movies.
Seventh, the movie is like a tribute to all Marvel movies before. Every movie is referred to and is remembered. No elements were wasted in any movies before.
Eighth, the comedy still being there though not dominating. It's arguably still a fun movie to watch (that was a lie it's super sad).
Ninth, the costume design and the setting were really enjoyable. It delivers perfectly everything we've seen in the comics before.
Tenth, the attention they give to time travel. I was worried that the time travel in Endgame would end like some illogical sci-fi movie like Back to the Future or Blast from the Past, but the movie realizes that and makes the time travel at least acceptable, though it's still illogical anyways.
okie I'm a Marvel nerd