Absolutely incredible. Even if you think you know what happens, this movie will shatter you. This final film to wrap up the Infinity Saga is an emotional roller-coaster. I started crying at one point and didn't stop until I exited the theater, it was just sad tears, then happy, wowed, fearful, and mournful tears. Sure, there's quite a bit of fan service, but none of it's completely out of the blue. It's so fulfilling to see all these heroes come together and fight. It spends a lot of time on the original Avengers and really develops them.
(That's about it for my review, below is me retorting to a deluded article about Endgame)
There's a ridiculous article out there saying that once the context of the film is removed, it makes no sense whatsoever to any first-time Marvel watcher, and that means it's "audacious" and my response is "Why, in your right mind, would you EVER think to watch Avengers: Endgame without know the backstory?" Marvel is well known for its sequential plots, and if anyone thinks they can watch Endgame and pick up every detail and recognize every character without having seen at least majority of the other MCU films, they are terribly wrong.
Endgame is a culmination of just OVER TWENTY films. It's a film for those who have waited so long to see all their favorite heroes team up against their biggest enemy. It is NOT a standalone and should never be seen as such (I'm very passionate about the MCU).
Tl;dr, Endgame is the most profound film for any devoted Marvel fan and deserves all the praise it's received.