Here’s what Warren Ellis said in his weekly newsletter:

So. INFINITY WAR, then. No spoilers.
It is perhaps best understood as an unprecedented brand power move. It is not “a film” as that term is commonly understood. It is a sequence of connections. It’s a statement from a bizarre place of popular-culture ownership. It’s a statement that they have done ten years of film storytelling, often with very conventional story templates, so that everyone in the world will show up for what is often an extraordinarily unconventional story-like event with one extremely unexpected tonal shift.
It, by design, makes no sense unless you’ve watched most if not all of the other Marvel films. There cannot be a casual viewer of this emanation. Only a committed one. It is likely to be the largest worldwide opening of all time, as I write this, even though it’s not opening in China or Russia this weekend.
The production values are near-perfect. The days of the slightly janky AVENGERS special effects are long gone, and every pixel is painted with jewelled, exquisite skill. As a visual experience, it is peak Marvel. The mocap on Josh Brolin makes Thanos a far more effective “CGI villain” than the waste of Ciaran Hinds on JUSTICE LEAGUE, which had all the performance nuance of a level boss in DOOM II.
Per the trailer, I think it was a brave choice to have the evil spaceship apparently designed by James Dyson.
The writers and the directors worked very, very hard to make something that did not feel beholden to rules. They’ll stop the thing dead for sixty seconds to do a gag. There are a lot of gags. I mean, no possible joke goes unjoked. Nothing I say here should be taken to denigrate the work of those people. They have achieved a remarkable thing.
(Special nod to whoever designed the sonics for the next-to-final scene.)
It is not a movie. It is a brand manifestation that wants to have prolonged, eager and reasonably skilled cultural sex with you. It wants your experience with its content™ to be satisfying and it hopes you are pleased enough to return for further interaction with the Brand. This is a very 21C thing. I like it for that alone, to be honest.
AVENGERS 4 happens next year, of course, and I will be interested to see how they stick the landing. But, in terms of cultural power plays, this one is the pinnacle.