It's just an ok movie. And yes, you need to watch all 21 to enjoy this fully.

Rating: 7/10 (26 April 2019)

There are two things that MCU got absolutely right in Endgame, it's marketing and the number of superheroes in the movie. Otherwise, it's a predictable, mediocre and just any other movie, made only for the fans with a lot of efforts. And I would definitely rate it lesser than Infinity War and Civil War.
Instead of making huge debate, I'll just prove my point in bullets below:
-They ruined Thor for everyone, he's just a comedy gimmick from now on.
-After watching A4, I believe the Infinity war should have ended at killing Thanos at his 'Garden' with Avengers losing 'absolutely all hopes'. That starting in A4 seemed pretty forced and misplaced to me, rather it should have started after 5 years.
-The whole idea of original avenger's stories coming to conclusion seems very forced especially Captain remaining behind in past.
-Natasha and Clint's so called emotional sequence where she dies, is one of the lowest point of the movie.
-Lets not even talk about Time Travel, I believe it was the easiest way they could write this movie. It seems very non sensical.
-Movie seemed burdened with its own weight of being emotional comedy yet action packed. At points you'll feel that it's unnecessary and even not that funny.
-One of the biggest flaw is that it's only made for fans, unlike previous 3 avengers. There are far too many references, that only fans will understand. As few critics put it, a fan service. Having said that, if you're a fan, you'll love it like hell.
-The final battle is the selling point, that's what all fans wanted to see.
-They did exactly what I was afraid of, undo the snap. Which translates to undo the previous movie. That's not something they should have done, again a lazy script.
-As engaging as IW was because of its plot, this one is only engaging for it's one liners. Again, that too only for fans because you won't enjoy if you haven't seen previous ones.
It's a good movie, but unfortunately doesn't live up to the quality of Infinity War. That's just sad.