After giving this some thought and reading/watching a number of reviews, it is clear to me that "Infinity War" is a decisive win for Marvel and audiences alike. This may be a unique franchise in film history - the likes of which we haven't seen before or perhaps since.
This film did well many of the things that "The Last Jedi" tried but failed to do. "Infinity War" made many bold, risky, dramatically high stakes choices. It leverages the long history of character development with its cast, doesn't bother to re-hash or summarize previous work and instead invests heavily in the development of the antagonist. This worked incredibly well and gave us an experience that finally addressed the "superhero villain problem" of a truly formidable, competent and coherent antagonist.
There was a moment when "The Last Jedi" really could have gone differently and committed to similarly bold choices. But it didn't. It quickly reverted back to the tired formula of the previous seven films. And that insulted the intelligence of an audience it had been preparing for more... and then delivered less.
But "Infinity War" did that. Thanos enters the film by assuring us that the Avengers will fail. It shows us mighty struggles within and between its impressive, fully-developed cast. It delivers on its promise while keeping audiences guessing as to how it will play out. And in doing so, this film shows us just how inferior a work like "Justice League" really is. "Infinity War" cashes in on the cumulative narrative interest into which we have been investing since Iron Man a decade ago.
Personally, I would have loved another 10 minutes in this already epic film to add story lines for Ant Man and Hawkeye just for the sake of completion. Aside from that, the film was a near-perfect juggling act of character, plot, setting, and theme. It's hard to imagine a better version of this film - the likes of which we really haven't seen before. And it perfectly sets up what will no doubt be a fully-realized conclusion with its sequel (currently slated for May 3, 2019). For most of us, that date cannot come soon enough and one longs for the Eye of Agamotto to speed up that release date!