From the collection of both good and negative reviews I've read, some also being a bit too apologetic as if they trying to excuse the negative aspects is basically this: THANOS rocks and often they claim is the BEST VILLAIN ever in the MCU. fukkin' Campea even made the outrageous claim that he's better than Heath Ledger's Joker which I have to see to believe that. I cannot fathom that at all. But the general consensus is that Thanos is the GOAT MCU villain to which is what everyone WANT and should be excited for that.
The negative consensus is that it is a shoddy storyline with a basic plot. They depended on too much sensationalism. Too many characters yet none get the proper screen time, mainly because the most is filled over Thanos. And it gets a bit Transformers Michael Bayish in many moments due to the excessive runtime alongside the excessive action. I suspect too much is going to be overwhelming. But that said, it is to be expected you have a gang of characters and therefore spread too thin and a lot of action.