Saw Infinity War, going to see it again in 3D probably next weekend. So far I would give it a 9/10. The only "critique" I would have is it seemed "choppy" story line wise at times but that is going to happen when you have like 20+ super heroes doing different things to at different planets/places to try to stop Thanos.
I will say that it is the first Marvel movie (ok, Thor:Ragnorok did too) that has a really Bad Ass villian that actually kicks the crap out of people.
It really is "dark" and you should really watch taking young kids to it, 2 different younger kids in my theater were crying pretty bad at the end of the movie.