I too have these omissions. Don't judge me. Provide recommendations instead.
If you want quality Marx Brother that actually feels structured like an actual film, Night at the Opera is the way to go, even though I prefer their earlier films where all attempts at storytelling and technical competence are annihilated by the sheer presence of the brothers. Duck Soup, Horse Feathers. Animal Crackers is also classic, but it is a real creaky relic.
Minnie and Moskowitz is likely the easiest film by Cassavetes to start with, but it's never really felt essential. To get that particular feel, you need to immerse yourself inside of Cassevete's indulgences, and just let him run the camera into the ground with endless minutes of improvisation. In this vein, Woman Under the Influence is probably the easiest to get into and understands its slow rhythms. Easily, the most emotionally satisfying.
As for the rest:
Husbands is his unique and self indulgent approach on steroids....or rather, lots and lots of beer and whiskey. Is the film probably most likely to put those unfamiliar with him off his movies forever. You got to build yourself up to this one. Regardless of the caveat's though, it's one of his best.
Killing of a Chinese Bookie is his slowfooted homage to gangster films. It's one of his more fascinatingly odd movies, with probably the most sad sack character ever put to film. I think by playing with genre though, a lot of people might get frustrated by this, because they might expect a little more action to happen. Cassavetes is going to Cassavette though, so don't expect him to give you much in that way. It's lethargy is partly why its so hauntingly fascinating though.
Love Streams feels like an accumulation of everything he had done up to that point, and so may be best suited to watching last. Probably his weirdest film.
Faces - very rough and primitive. But kind of sets the table for everythign he was going to do. Just grab a camera, find someone interesting, and just stare and stare until they do something. Very good
Shadows - Fairly easy to digest. Feels almost like a 60's student film. Has a quicker pace that most of his movies, but I don't feel he quite had a handle on what he really wanted to do yet though.
Gloria - Interesting, but far from essential
Opening Night - I've never got much out of this one. I should probably revisit it at some point.