I feel the same way about the ending.
Loved the movie on the whole, but because of said public knowledge we know of, it made the ending seem like it meant less and I walked out of the theater feeling a bit more down on it than I was while watching the movie because of it.
Oh, and btw, I love big movie openings like this. Going and meeting other people that love what you love and hearing the reactions from the audience during certain moments is always worth it.
My friends and I made the same comment. Why they decided to change the name of next years film I guess i'll only be able to understand if the new name makes more sense for Avengers 4 than "Infinity War".