I just got back from seeing it and agree with some here that the first and final acts were great, but that middle act with the time travel really dragged in my opinion. I had really been looking forward to seeing how they explained Dr. Strange giving up the time stone without much resistance, then was pretty disappointed with the resolution. It just left me thinking 'that's it?'.
I was also a bit disappointed in Captain Marvel, they built her up in her own film as being probably the single most powerful character, so I was looking forward to seeing her take on Thanos and also just generally interact with the other characters, but then she barely features in the film at all. Also, that bit where all the main female characters team up to try to get the gauntlet to the van was really cringey and a bit patronising for women imo.
All-in-all it was still a satisfying conclusion to phase 3, particularly with the way it ended for Iron Man and Captain America, but I thought there were parts of the film that were a bit of a letdown. Certainly not the best Marvel film, but not the worst either.