It's probably the best if you watch it right after watching Casino Royale. QofS is a continuation of CR and takes place just a few hours after CR ends.
And it gives a finality to the story of his pain over Vesper and heals Bond from the vengeance that is eating away at him. In the end, he has closure and doesn't end up killing the last guy.
It's the only reason I will own QofS (when the price drops
), in my opinion it's not a good stand alone movie, it actually almost lost me when I went to see it, but I really liked how it ended. And I was glad I refreshed my memory by seeing CR before I went to see QofS.
So yeah, if you liked the
story of CR, not just the action, it's well worth to have.