It becomes really tough to tell a compelling story when A Cosmic Level Stress upon Humanity is the only sheer element of a Narrative.
But the way marvel has dealt with it.. is just Splendidly Ingenious! They made a Complex villain with unclear/unrevealed Motives that kept people hooked and give a second thought to their perspective. we were all expecting Thanos to be a Villainous dore who kills because it makes him feel good but the Movie actually revolves around him only, it's an Antagonist centeric movie who isn't actually evil.. just his vision isn't as narrow as ours he tells how insignificant our existense is against the Fate of the Universe, To save it he plans to wipe half of the life from Universe that will make it more balanced and steer
The Avengers on the other hand don't get much screen time. Captain has almost no idea what is going on, Tony has nothing but his Nano Tech Armor, Bruce cannot Transform..Thor on the other hand manages to shine while joining the Battlefield other than that he also fails to avenge his people (at least in this part)
Overall, it's a great film arguably the best MCU film till date though like everything else in the universe, this movie also has its drawbacks Characters like Ebony Maw seemed promising on the surface but couldn't survive the irreleving screentime also The Black Order (Children of Thanos) didn't seem connected to their master but again it's better to dispose extras than rushing things up.