ROTJ is one of my three favorites and it's yards better than any of the prequels or sequels. I'd put it above ANH, actually. But to me, ESB is in that category of "perfect movies", like Casablanca & Princess Bride... movies that know exactly what they're trying to do and pull it off without a hitch.
Doom/Doom II. Already been playing it for 3/4 of my life, and the modding community still keeps it fresh so even if the core game gets old, there's still things to do with it.