Great stuff. Bring on Avengers 4!

Rating: 8/10 (28 April 2018)

The end of this movie gives new meaning to the phrase "done and dusted", though I can't explain that without a spoiler! No doubt at all, you get your money's worth. Infinity War pulls you right in, there's never a dull moment, and it's every fan's dream to see this many heroes all at once. I'd say the strongest part of this one is just how well all of them are managed. Still -- I'm going to hold back giving this a numerical rating for IMdB till I see Avengers 4 next year. (Note added a year later: I've seen Avengers Endgame now, and I rate them both 8/10. Endgame is splashier, but Infinity War has a more tightly constructed storyline that is handled masterfully.) It's not giving anything away to say that these two movies are a duology (or actually a duology with a prelude, which is Thor Ragnarok: the action bridges seamlessly from that one to AIW.) Some things happened in TR that I wasn't fond of, but they turn out to be resolved anew in AIW. It sets up some big new problems though, so how effective AIW turns out to be will depend on how well they bring it home in A4. People who want to judge this one harshly -- just wait. This is only the first half of a bigger story. I've got my own ideas about how it's going to shake down but there are already a bunch of "theories" being floated out there on the Web.
OK: in short, this one raises the bar yet again for the genre. Marvel has a smoothly running machine that knows how to turn out a well crafted product; and I have to give their writers and planners credit for thinking way ahead -- concocting plot arcs that unfold over several films. Full credit as well for giving us a fantasy world so absorbing that you kind of have to shake yourself back to reality when the credits finally roll. I felt the same sort of way with the Lord of the Rings trilogy (the original three, not the Hobbit trilogy). Each of those three films was about 3 hours long, complex, layered, and interlocked. Is AIW at the LOTR level? No. The LOTR films were a bloody miracle. But the new Avengers is darn good.
After the terrific success of Thor Ragnarok and Black Panther in just the past few months -- along with CA Civil War (2016), which was functionally Avengers 2.5 -- it wasn't clear what they could do to top all of that. And maybe if AIW turned out to be "just as good", it could still be counted as a win. But it's better. The CGI is state of the art, the jumps between the multiple plot lines are expertly timed, and since almost all the characters are already familiar they don't need backstory time. After the first 20 minutes of so of dramatic entrances, you can just settle in and watch them go. The characters that do need introducing are the villains -- Thanos himself, who isn't actually in every scene but somehow feels like he is, and his powerful Black Order minions. Thanos has plenty of time onscreen to develop his backstory and goals, but the four Black Order chiefs are given zero backstory, essentially there to give several of our heroes something to fight.
And about the heroes -- it was great to see Dr. Strange, Scarlet Witch, and Gamora being given the screen time and status they deserve. Some others may have been shortchanged, though that might mean they'll have bigger roles in A4. Benedict Cumberbatch, Elizabeth Olson, Josh Brolin are superb actors, Tom Holland is good and getting better, and all the rest of the cast are more than competent. And for me the surprise of the whole film was Peter Dinklage's role, which takes the way he's shown in his other movies and delightfully stands it on its head. However, in this kind of movie the best actors won't be used to their full potential anyway, because the story itself is the main thing and they are all there primarily to keep it moving. Brolin does nicely at raising Thanos from a one-dimensional character to 2-dimensional (can't really expect anything more in superhero movies) as someone with a past and with strong reasons for his actions. He's an evil man doing the good that good cannot do (If I recall right that quote is from a Mickey Spillane novel); it's just that his idea of "good" involves erasing half the living beings in the universe.
Two other little complaints: the words 'galaxy' and 'universe' are used interchangeably (which is like comparing a grain of sand to the whole Earth). And there's a certain CGI effect repeatedly used toward the end that is directly borrowed from X-Men The Last Stand.
All in all, it's great stuff. I'd go and see Avengers 4 right now if it was available.