Well, first of, you must know what 'Close Encounters' are; then what 'Close Encounters of the 1st, 2nd, and finally 'Third Kind' are. The differences between them, etc.
Watching the movie by itself with no knowledge of UFO history or myths or lore wouldnt do much for anyone.
Ifcourse, 2001:A Space Odyssey is still the best sci-fi movie ever made. Yes, it's confusing, and slow, and doesnt make sense at first; what's the big black thing, why are the monkeys fighting, why does HAL kill all onboard, what is the white room, why does the old man turn into a baby which then somehow floats in space above planet Earth, etc.
But, Close Encounters of the Third Kind was in fact surpassed by Star Trek, Star Wars, Blade Runner, ET, and many others in popularity.