Sweetgrass is my go-to spa when I want to splurge on myself (or more likely, got a gift card for my birthday/xmas as I generally always ask for one). It's far from perfect, but I find the pros outweigh the cons, and I always feel so relaxed sitting by their pool area after my treatments.
Some of the pros:
Beautiful pool/hot tub/sauna area that looks sort of lagoon-like.
High quality treatments and services.
Really nice staff, who don't push expensive products on you (aside from this one time, but I ended up buying the product so I guess she was just a good saleswoman).
The changing room/shower area is nice and clean.
It has never been too crowded - I almost always get ready in an empty changing room.
Some of the cons:
$$$
It's women only, so can't do a couples massage or anything (well, this may be a con to some ppl - I actually enjoy the women only atmosphere).
No convenient parking nearby.
In the immortal words of Donna from Parks and Rec... Treat Yo' Self!