I didn't expect it at all, and it was quite a surprise. So basically, half the intelligent population of the entire universe is gone (even though the determination who lives and who dies is quite difficult to believe).
Although I'm sure the next movie will reverse time before Thanos clicked his super fingers and the Avengers will strip him of his power gauntlet, I'm sure. And with no repercussions, neither.
the only thing I knew for sure was that Loki was going to Die at the beginning, I had not been spoiled but was certain by The Trailers that it was going to happen
I knew the Ending was said to be Haunting,Devastating and Emotional, I figured it had to End With Thanos Snapping his fingers and half of The Universe disappearing, I knew nothing Of what heroes would go or how....even though I expected it, It was done so well and masterful, I still Felt Floored...
No Clue about Heimdall, Gamera or Vision, No Clue about Red Skull, Or Captain Marvel...
Most of all though, I had no expectation of just how truly Great Thanos would be....for me personally, Theres not anything that could have been done to make me anymore impressed with Thanos
I came away concluding Thanos is the greatest threat ever put on screen in a CBM(the 2nd greatest villain in a CBM behind Ledgers Jokers) and The CGI work on Thanos is for me one of the best examples of a CGI character I've ever seen....
Also, so glad I wasnt spoiled or even had a hint that Hulk Vs Thanos takes places in the first 5 mins....
They literally did a Masterclass in showing how to introduce a Villain and instantly make the audience understand how Power,deadly and threatening he is...
Having Thanos Beat Both Thor and Hulk(and specifically show Thanos Dominate Hulk in a Fight, and Show him do in Hand to Hand combat) then have him Kill Loki....for me, It may be the best start to any CBM ever and by far the best Introduce to a villain ever!