Good call.
I suppose a Onewatchable can fall into different categories - upsetting first time and will be again forever after (Schindler's List is a great example); a film that relies on The Twist (The Sixth Sense perhaps? The Usual Suspects? though you might watch it again to see 'how it works'); something that would/might lose something of its joy the second time around (my mum has refused to see ET again since the 80s for that very reason, although I have and still cry at the flowers every time).
The usual suspects is one of my favourite films and I've watched it more than 5 times.