My take after a 2nd viewing (spoilers)
The good:
Death of Iron Man: The way they did the death and funeral of Tony was quite effective and emotional. This is probably one of the most powerful superhero death's ever, i think it beats out Logan's death. The funeral scene with the message to his daughter nearly had me choked up, and that is not an easy thing to do.
Death of Black Widow: the scene of her death was well done and i felt it was a great emotional close to her character. I think it got glossed over a little to fast after they got back, but it felt like a great arc to a interesting and complex character.
The management of the epic scale and huge cast was done just remarkably well, they had an even bigger cast to juggle than infinity war and I think they did so with even greater success.
The Time Heist was one of the most interesting ways I have seen time travel handled, despite the fact that there are still holes in it, it did a good job of maintaining what feels like logic and consistency within the universe; not perfect but good.
Action sequences were remarkably well done and what could have been messy hard to see action was not.
Nebula and the actress's performance was awesome, she just became one of my new favorite characters. The scene where she had to kill herself was messed up in the most awesome way. And though Gamora was only in this one for a short time, I really like how they brought her 'back to life'. Both funny and true to her character.
A great closing to the Marvel Cinematic Universe.
The Bad:
I hate what they did with Hulk. He was so boring and did not really add anything to the story other than being a plot device that could us the gauntlet and survive.
Captain Marvel was an awful character. I have not seen the Captain Marvel film yet, but are they intentionally making her as pretentiously smug and unlikable as they can? I am glad she was only in for a few minutes.
The 'girl power' scene (though short) was pretty obviously forced and really took me out of the scene for a few minutes. (before any claims of misogamy are cast my direction, I encourage to read above about my praise for Nebula (now my favorite surviving character), Gamora, and Black Widow.)
Thanos's objective changed wildly from wanting to eliminate half the population and letting the remaining population flourish to destroy them all and start over. This removed one of the more interesting aspects of his character, which was no more death than what he thought necessary, this change in objective made him more generic and boring.
Also his power level was wildly inconsistent. He seemed more powerful in this than he did with all 3 to 5 stones. His army and generals were wildly underused in the final battle. Too much focus on him without the stones and his strength to battle off as many and more enemies than with the stones added to the inconsistency. Thanos's generals should have been more involved in that fight.
The Ugly (or honorable mentions)
The Thor fat and pathetic story line became redundant and painful to watch after about 10 minutes. It was fine for a few laughs but they should have moved on from it faster.
Gamora was notably missing from Tony's funeral and the entire end of the movie. Unclear if she went back to her timeline or not.
Timeline seems all screwed up. They returned the stones but now Thanos is missing from the 'prime' timeline. So the the time branches theory doesn't seemed solved by returning the stones to their proper place in time.
Captain America ending was odd to say the least, I do not know if we are supposed to think he lived out a separate time line (alternative universe) or if he lived in the prime and stayed non-involved throughout the 20th century to avoid messing up the timeline.