Citizen Kane is beautifully made and, at the time, rewrote the rules of filmmaking. The story itself is interesting but not exactly captivating. I think the film has some entertainment value but is more valuable as a historical marker.
Seven Samurai is the only Kurosawa samurai film that I can stay awake through. Really enjoyed Rhapsody in August, though.
Casablanca is not only impeccably made but still highly entertaining. I loved every minute of it and can't wait to see it again soon. However, for pure entertainment value, I prefer The Maltese Falcon. It blows my mind how some movies could be so intelligent (and some people might say vulgar) in the 1940s.