Very difficult to discuss without spoilers. I'd give it a 9 out of 10 if you're a fan of the Marvel movies in general, but I don't think there is enough there on its own to be the kind of movie that will change minds. I recommend Black Panther even to people who don't like the previous Marvel movies. But this movie is definitely one for the fans.
I liked the MCU version of Thanos. Infinity War is a rather unique creature among superhero movies in which the villain is the protagonist of the movie. It is Thanos who has the strongest character arc, and it is paid off in the movie. If you think about the movie that way, the movie ended the only way it could end.
I liked the way the movie handled the characters in general. It seemed remarkably balanced for a movie with so many characters. But a lot of the credit for that goes to Marvel Studios for continuing to build on their cinematic universe. If you've seen the previous movies and have come to know and love these characters you can hit the ground running. If not, it could seem to be a blurry jumble to a newcomer. If there is such a thing.
I liked the way that in one sense its obviously the first part of a longer story, and in another sense it is one stand alone story. But there's no way to discuss that spoiler free.
Amazingly, I liked the fact that the trailers both hyped the movie and yet didn't give away many important beats to the story. That doesn't happen often these days.
I personally liked the way they used humor to help pace the movie. Infinity War is extremely dense, and it moves rapidly from one scene where a lot is happening to another scene where a lot is happening. In some movies (say, Winter Soldier) the action and activity is interspersed among slower scenes where the audience can catch their breath. In this movie, you don't get very many such moments. The banter and the humor make sure you don't get wound up too tightly for too long. It can be a little distracting at times, but I think that's deliberate. You're meant to get slightly kicked out of the scene to have a laugh and then jump right back in.
I liked that the movie defied expectations. It did that multiple times. I won't say more about that.
There's two moments that I think some will think are dumb. The second one didn't bother me, because I believe that there was a very good reason for it set up earlier, where the character in question is doing an apparently dumb thing for a good reason we just don't know. In fact it is so obviously out of character that it plays as a deliberate act of subterfuge. The first one made me literally think they should have
just eaten Gilligan. If i was there, I would have literally shot him in the face.
As I'm watching the credits roll waiting for the stinger, all I could think was "wow, I really just saw that." If you are a fan of the MCU, go see this movie. If you don't have excellent bladder control, don't drink the big drink: there are very few bathroom break moments in the movie. Don't read spoilers. Don't read anything about the movie until you see it. See it with fresh eyes. Infinity War is as much an experience as a story, and you'll want to get the full experience of just watching it all happen.