Saw it last night- great fun for the first 2/3rds, lots of humour and excellent, comic-book style action. But that ending was a major bummer and I there was a sad pall over the cinema when it ended. It's a real Empire Strikes Back.
Yeah. We saw it Friday and had a similar reaction.
SPOILERS
Lots of good lines. The Guardians and Nebula were amazing. Banner was great. Strange and Spidey were fantastic, as were Vision and the Scarlet Witch. I agree with the poster who said that Thanos was nicely fleshed out; his motivation almost sounded rational. I was pleased to see that I was right in my suspicion that the Red Skull survived. Eitri is magnificently realized.
Somewhere someone said words to the effect that Vision and Scarlet Witch are going to represent the emotional heart of the film. That clearly wasn't the case, as it is Thanos and Gamora who do. I didn't find how Thanos got the Soul Stone shocking, because it was telegraphed really well; with the whole audience (or all of the adults, anyway) Gamora wrapped in the last vestige of her innocence was the last to know. That was pretty devastating nonetheless.
I kept expecting a quick wrap-up and was surprised that there was no resolution, which for me is part of why the comparison to TESB is apropos. The rest would be that the bad guys won.
Fear not, though, Captain Marvel has been summoned!
No seriously, though, this is a pretty dang humongous cliffhanger, way beyond Han being frozen in carbonite and not knowing about Luke's father. There's a pretty high bar set for how to resolve this.
This is worth seeing, and for being entertaining start to finish and having mature emotional content it gets an A+ from me.