If I Were a Russo Brother...
Obviously, Spoilers....
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I enjoyed Endgame immensely, and think they concluded it in a great way. However, if I were a 3rd Russo Brother...
Have Thanos show up and blow up Avengers HQ before Hulk puts on Stark's gauntlet and undoes the snap. That seems to give a lot more weight to the final battle. It also means the battle will just be Thanos v. the remaining original Avengers.
Having seen the movie but once, I can't perfectly recall the sequence of events leading up to Captain America wielding Mjolnir, but I recall it being Mjolnir striking Thanos then returning to Cap's hand. Before that moment we were unaware he was about to attempt to use the hammer. I think one extra scene would have added both clarity and intensity: as Thanos is overpowering Thor, and about to kill him with Stormbreaker, pull back and show that fight from Cap's point of view. Then, have him turn his head and focus on Mjolnir lying inches away. Cut back to Thanos/Thor and THEN have the hammer fly in and strike Thanos, then return to Cap's outstretched hand. I could well be wrong, but I think that one moment would build massive anticipation, and up the ante on just how epic the moment was about to be.
As for the final battle, while I understand the idea behind having every single MCU hero face off against Thanos' entire horde, we already had something similar in Infinity War. Don't get me wrong, Endgame's battle royale was amazing, and it worked, but I would have liked the small-scale battle of Thanos vs. Captain America, Thor, and Iron Man, to have been the finale. When it came down to Cap standing up, alone, tightening his shield, and giving a look of gritty determination that is on par with maybe any such look in the history of cinema, I wanted to see Cap use Mjolnir to give him the strength to go toe to toe with Thanos and pummel him. He was the first Avenger, and it would have been poetic to see him stand alone as the last Avenger and defeat Thanos. Then they can dig through the rubble, find the Infinity Stones, and undo the snap.
Again, loved the film as it is, this is just how I might have given it a less is more finale.