I cried. I smiled. Then I looked at my watch and wondered when it will end. Did it have to be that long? I left the theater thinking about the size of egos and the amount of self back-patting that went on in the making of this film. This film is so important because we are so important so darn it we will make a 3 hours long movie that tells everyone how great we are via a review of all the movies we made. Did the movie have to be that long to NOT explain how Thanosโs seemingly large planet-conquering army is really too small to conquer a planet especially if they use hand-to-hand combat as the primary mode of warfare (the scale of the force is reflected by the fact that they only occupy a chunk of land where the Avengers Headquarter sat). So what, they take the Burroughs then Manhattan then move to Long Island? Wow. What happened on planets that were bigger than Earth with larger land masses and larger populations?
Not explained would also be the fact that of all advanced races out there such as Shiar, Skrull, and Kree, only one space-faring being entered the fray: Captain Marvel.
Not explained is why one would need all Infinity Stones as opposed to just Reality stone (wish a new reality where everyone lived and no Thanos) or the Time stone (go back in Time and stop Peter Quill from slapping Thanos awake so his glove could be removed). The same strategy could have been used by Tony Stark. He did not need to take all the Stones to 1: Keep Thanos from being able to snap his finger and 2: Defeat him (take the Power or the Reality Stone and Thanos canโt snap his finger and use it to defeat him and his army AND no Gamma radiation death).
Not explained was how Thanos shrank his ship and entered the Quantum Realm. If that knowledge was available to him he could have used it to obtain the Stones in the first place.