I definitely wasn't expecting it to be as good as it was and I agree that we got a pretty good payoff, they could have maybe built Thanos a little more in the previous films though because it felt like he just came out of nowhere for the most part.
I hope Strange has something up his sleeve otherwise that choice was just idiotic, Quill though was a complete moron for that, no excuses! Thanos definitely has a flawed plan no arguments there but I believe that he believes it will make things better.
Spoiler warning added!