My thoughts:
Great movie, with several buts:
--Anytime you bring time travel into the equation, you've basically invalidated the "seriousness" of the movie. Obviously the mass deaths at the end are going to be undone, considering several "dead" characters have upcoming movies already in the works. So there wasn't much emotion involved for me at all. Now, do I think Vision, Loki, Gamora, stay dead? Probably. But we'll see.
--I don't buy into at all the thought that the "old" Avengers will be whacked in the next one while the "new" ones return. I just can't see the sense from a merchandising perspective that you'll just kill off Thor, Captain America, Iron Man, etc. Plus I hope they don't want to go the full-on DC Comics "let's be so dark everyone hates us" route. I think it's much more sensible that the rest retire in some way and hand the reigns to the younger bunch. Besides, I think Part II will be much more the Avengers kicking butt.
--I thought the post credit scene misfired. Probably 90% of the theater I was in was like huh? what? what's that? They didn't know what the logo was or what it meant, so it had little impact I thought. And on that score, if Captain Marvel is essentially the Superman of the Marvel world, if you're facing an apocalyptic villain that's wiping out billions of lives, wouldn't you make that call to your ultimate hero a little sooner?
Anyway, liked the movie a lot just didn't like the ending.