The stand-out performance is, obviously, Ralph Fiennes, as M. Gustave. There is a plot but this film is about style (especially its almost animated design) and performances. Fiennes has the most screen time and he has to carry large portions of the film on his back. His character's predilections might not seem those of a sympathetic character but Fiennes sells it. He never chews the scenery either. He isn't alone in delivering--F. Murray Abraham, Willem Dafoe, Harvey Keitel and especially newcomer, Tony Revolori are all great in roles of varying sizes.
Sometimes an "all star cast" should be looked on with caution. Many directors/producers seem to think that throwing a bunch of names at an audience is enough but Anderson gives everyone something to do--even if they are, literally, in the movie only for a few minutes. He seems to get the best from everyone.
If Charles Chaplin were alive today he would be making movies like Anderson. Neither director was afraid of sentimentality--and indeed both are masters of it. A comparison to Chaplin is pretty close to the highest praise you can give a filmmaker. Some will see this film and think; what's the big deal? But it is.
I would suggest looking at all the big budget epics who spend hundreds of millions to "create a world" and fall on their face in a pile of CGI. Anderson, here, has made what is quite similar to a cartoon and he succeeds without a hitch.
A fine film and one that begs to be seen more than once.