SPOILER WARNING: this list takes a deep dive into some of Infinity War's most ill-advised details. Proceed with caution.
By now, you’ve had time to digest Avengers: Infinity War, so you've probably realized it didn’t make a whole lot of sense. After a long string of successes, Marvel was bound to slip up at some point, and unfortunately, Infinity War doesn't live up to its predecessors. The reason why Infinity War is the weakest Avengers movie cannot be reduced to a single moment, as it's a big, big film.
A few critics who caught the film's midnight premiere left the theater exhausted and filled with Infinity War critiques,. A lot of people are left with unanswered questions about Infinity War, and judging by th plot holes, creators are seemingly okay with leaving things unexplained. While it can be fun to turn your brain off and watch actors smash CGI aliens, once you try to make sense of what's happening on-screen, you might agree that Infinity War missed the marka bit.
Thanos is the big bad of the MCU, so he has to exist in multiple storylines, and the easiest way to get him back and forth is to have him teleport. His ability to be wherever he wants makes him a huge threat, but it also forces viewers to wonder why other characters' teleportation powers only work when it's narratively convenient. Doctor Strange and Wong have abilities similar to Thanos's, but there are several key scenes in which they seem to forget this.
Wong even manages to cut a guy's arm off with his powers, so his inability to do the same to Thanos is incredibly frustrating.
One of the biggest plot holes in Infinity War comes after Thor shows up on the Guardians' ship, gives them some info on Thanos, and says the villain is going to Knowhere to look for the Soul Stone. Gamora happens to know where the stone is, and says she needs to stay as far away from Thanos as possible to keep the location a secret. Then she goes to Knowhere.
The plot requires Gamora to wind up in Knowhere, as she needs to be captured by Thanos, but that's not good storytelling. If there had been something driving her collide with Thanos, it would have made more sense, but as it stands, she voluntarily elects to do the exact thing she said shouldn't happen.
Aside from his position as franchise antagonist, the story of Infinity War provides little explanation for why Thanos wants to wipe out half the galaxy. In a flashback, Thanos says he watched his world die from a lack of natural resources, so he decided to kill half of everything, leaving the rest to prosper. It seems like it was a tough call to make, but he figured the surviving half of the universe wouldn't mind, and felt the Infinity Gauntlet was the only way to accomplish his task.
The thing that trips up a lot of viewers is, once Thanos acquires the Gauntlet and all of its Stones, he never considers using it to create additional natural resources, instead of murdering everyone. Josh Brolin portrays Thanos as an intelligent villain who believes he's doing the right thing, so it's odd he never reflects on his own ability to change reality to fit the needs of the galaxy.
The events of Civil War see the MCU heroes split down the middle, with Tony Stark and Steve Rogers on opposing ends of a philosophical argument about the role of government in the lives of superheroes. In the film's finale, they come to blows, leaving audiences wondering how they could reunite in Infinity War. Unfortunately, the plot line is pushed to the side, and fans may never see a resolution to the issue.
In an interview, one of the writers of Infinity War, Stephen McFeely, confessed the beef was glossed over to save time, saying:
Our first sort of wonky draft [had] the idea that they had to get back in the same room together and deal with that... [But it] meant that you’re slowing down your Thanos [Infinity] Stones [quest] to deal with other threats from other movies. And... it became clear that this movie needed to be propulsive and be about Thanos and what he represented to the Avengers.
While this it's understandable, it furthers the idea that Infinity War tried to do too much too fast. Propulsion is important, but the 19th film in a franchise should not jet past major conflicts from previous movies.