I LOVE this day spa. I've been to the spa at Bellagio and the Hilton. This is the best. I always do the day pass, but have not had any services, so I can't comment on that.
The four plunge pools, steam room and sauna are in great shape and a joy to use. The lounge chairs are always available and there is a large selection of magazines in the jacuzzi and the quiet area.
There are bottled waters, juices and a snack mix at the front desk. I have to say this is the best place in vegas to completely decompress!
The Fitness area is very good as well, although I think the Bellagio gym is a bit better. But overall Mandalay's Spa wins!