I've seen several fine films on the subject of Alzheimer's, including the excellent Canadian film "Away From Her" with Julie Christie (who also won numerous awards for her performance); "Still Alice" with Julianne Moore as a linguist who comes down with the disease; and a documentary called "I'll Be Me", about the singer/guitarist Glen Campbell, who eventually died of the disease, although he continued to perform (with monitors to read the lyrics he had forgotten) long after he came down with it. (Oddly, he remembered how to play guitar long after he forgot the songs).
But what sets "The Father" apart is that, unlike those three other films, in which one merely observes the sufferer, here one shares his experience, as it were from the inside out, even though one continues to be an observer at the same time. This is not apparent at first, but becomes so as the film progresses; and it is a shattering experience. One of the best and most disturbing films I've seen in some time. Olivia Colman is great, as always, and it's possibly Hopkins' best performance to date.