On Saturday afternoon, I went in theaters to see the finale of the "Infinity Stones" story arc of the Marvel Cinematic Universe. Avengers: Endgame is the cinematic event of a generation, as the movie that 21 movies have built up to. I will do my best to explain my opinion of the movie, and I'll do my best to avoid spoilers. (For this one; expect many spoilers for Infinity War, because this is a direct continuation from that movie.)
The movie begins in 2018, very shortly after the Snap. If you've been living under a rock since April 2018, here's the short of it: Thanos has succeeded in gathering all six Infinity Stones, and has snapped his fingers to destroy exactly half of all life in the universe. That includes superheroes, and that's not counting all of the characters who died prior to the Snap, whether it's in Infinity War or in films that came before.
(For the record, everything I've written here is either shown in trailers, or a part of Avengers: Infinity War, so there aren't major spoilers for Endgame in these paragraphs. I've made sure of it.)
The remaining heroes are left to pick up the pieces. It is the first major battle that they lose. Tony Stark is trapped in space with Nebula (an ally to the Guardians of the Galaxy), aboard a spaceship that has run out of fuel, who knows how many lightyears away from Earth; Steve, Natasha, Thor, Bruce, Rocket and others are mourning the ones who have been lost. Getting together in support groups, trying to regain a sort of meaning to their lives... On his end, Hawkeye has changed radically, now acting as a vigilante.
After his plan was successful, Thanos has retired to a farm on a distant planet, content with his achievement. The Infinity gauntlet now broken, the six Infinity Stones still in his possession (or at least, so everyone assumes), enjoying life after his twisted modification to the universe.
With the addition of Rocket and Nebula to the roster, the Avengers may have a way to go to space and, who knows, fight Thanos and defeat him this time. There is a way to undo what's been done. However, this would require the Infinity Stones...