I'm trying to remember the details, which is shameful since we just ate there last year. It's very cozy - curtains, plush carpet, etc. It's also very quiet. If you have a table by a window (request it) you can watch Illuminations.
I'm sure there are photos of it somewhere on this board.
We've eaten in almost every signature restaurant on the property (except V&A as I refuse to pack a suit or sports jacket), and the Bistro was by far the most romantic and quietest of them all. The food is pretty good, the desserts are excellent, and the wine list is awesome. Cost wise, I think it's on par with the other signature restaurants.
We're going this Dec as a group of 8 - all adults - and we took the Bistro off the list simply because it's just not the type of place for a party of 8.