It's really dependent on your tastes. It appears the US version of Citizen Kane is vastly superior to the UK but whether it's a must own is up to you.
Others I'd put in my must-own list, but possibly not yours:
Casablanca 70th anniversary edition (still can't believe the UK steel didn't have this)
Studio Ghibli titles
Watchmen Director's Cut (for the Maximum Movie Mode)
|