In fact, watching Casino Royale right before viewing QoS is almost required viewing for anyone going to see QoS in the theaters
Indeed. And I know quite a few people who went into QOS without having seen CR, or being aware of the new direction of the Bond movies. They would have been totally lost as to what they were watching.
I saw QoS with a friend and neither of us had seen Casino Royale.
(I had given up on Bond in the Dalton/Brosnan ere, I watched QoS because it was starting at the right time and we didn't want to hang about for later film).
Neither of us had any problems following the plot. We had both seen the QoS trailers when seeing other movies and that was enough really. The plot was fairly straight-forward and, as I say, neither of us had a problem.
I then went out and bought CR and watched it prior to seeing QoS for the second time. Certainly, watching CR added to my enjoyment of the second showing, but it didn't really add anything essential to QoS that I had not figured out for myself in the first sitting.
It was the fact that QoS is so very different from previous Bond movies that pulled me back into being a Bond fan.