"Yes, among the 9 movies nominated for Best Picture, there were at least 5 or 6 that were swell, but look at the rest of the list of ALL the movies released last year-- where are all those brilliant also-rans that were equally deserving but got snubbed due to lack of space?"
Someone, first it's not as if most movie years are brimming with brilliant also-rans, particularly of the awards-likely category of movies.
5 or 6 of a group of 9 being swell, if we were for the sake of argument to agree on that, is at least par for the course and at most bordering on a movie banner year. Even going back to vintage Hollywood one can find ****ty movies nominated for best picture, and even winning (The Greatest Show on Earth anyone?).
As far as movies not nominated for best picture that were well received (and we may not agree on all of them - when do we ever agree on all of them? that's what makes moviegoing) for your consideration: Indignation, Eye in the Sky, Toni Erdmann - these first three btw are standouts for me personally - Hail, Caesar! - in my opinion vastly underrated - Elle, Jackie - two movies I also liked very much and Huppert's destined for legend performance alone should make Elle required viewing - The Handmaiden, Loving, Jungle Book, Captain Fantastic, Silence, Love and Friendship. To name just a few.
I'll also add that one movie nominated for best picture, Hidden Figures, I would hardly call a great or oscar worthy movie. But for its genre, the middle of the road historical feel good movie, it was highly satisfying, well made, had some excellent performances, and didn't insult anyone's intelligence - which is a damn side more than I can say for a great many movies that win Oscars and a damn side more than what one can usually say for movies of its genre.