The facilities are well worth the price especially if you are thinking of purchasing a day pass. Very professional and friendly staff.
I had a facial, which is the reason for my 3 star rating. The facial itself and the service I received from the aesthetician was average at best.
Tip: if ambience is most important to you and especially if you are staying at the hotel, you can't go wrong with Bellagio spa. However if you are concerned with making sure you absolutely get your money's worth for both service and ambience, I would suggest venturing out to encore, where I've had consistent above average service and excellent spa ambience.