Claunchy,
Nice review. Delmonico's in Vegas is a perfect example imo of non-stuffy high-end dining. It's nice and classic and classy, while at the same time not feeling old. It's lit at a nice level, not too bright but not such that you have to squint to read the menus by the candle. The only black mark for this restaurant is the bathrooms. The men's is a pretty small restroom that is tucked in the back and is fine, but I expect it to be more perfect at a place like this. Service, as you mentioned, is great. You didn't mention one of my favorite touches at this and some other high end restaurants, how everyone gets their plate put on the table at the exact same time.
http://www.venetian.com/dining/menu_delmonicodinner.cfm
You really can't go wrong in the apps and soup/salad section. My personal favorites are the foie gras, the wilted spinach/fried mozzarella (basically the opposite of a salad), and tomato/onions/blue cheese plate.
For dinner the bone-in ribeye is definitely the way to go.
Every dessert I've tried has been great too.