As of this writing the Canyon Ranch Spa is too large and easy to get lost if you're coming from the Palazzo side. You would think it would be great because its conveniently located right off the pool area but do yourself a favor and enter from the Venetian until they (hopefully) get all that stuff worked out. You literally feel like you are walking through an big office complex and there is very little (and confusing) signage to help you along. We actually had to turn around and go back to ask if we were going the right way!
When we finally made our way around to the front, things were okay.. but really just okay. My (hugely overpriced) massage was nice enough but once again, in order to get to the massage rooms I felt like I was walking through an office building, not (what should be) a nice retreat space. There's absolutely no atmosphere to speak of. Very off putting.
My massage therapist told me that due to the addition of the Palazzo Tower they will eventually be the largest spa in the world at over 100,000 square feet... but that's not necessarily a good thing.
They have the requisite citrus waters and teas and yadda yadda but IMO, the money would be better spent on upgrades to the personal hygiene products they provide and lockers that don't take 4 tries to open (maybe that was just my particular locker but it sucked nonetheless)... etc etc.
I cannot comment on their other services, like exercise, salon, et al... but so far Bellagio still has my favorite spa, hands down.