The W Retreat is very highly regarded in Bali, and I can see why.
From the main street of Seminyak, you enter a beautiful bamboo driveway and feel instantly separated from the street, even though you are no more than $3 USD taxi away from anything in Seminyak. The architecture is most interesting, a little 60's modern, paired with the typically Rockwell designed W vibe. We stayed at the main building so cannot comment on the villas. From what I can tell, they seem quite far and might require a buggy to bring you to the main building, where everything else is.
We were in a ocean facing guest room which was beautifully appointed, all tricked out with ipod docking station, free wifi, glass shower, free standing tub, etc. It was a little annoying that the toilet itself was also behind glass, which made using it a little, well, uncomfortable. Also of note is that since the W has a party vibe, the music from the Woo bar is pumping well past 11:00 p.m. So, if you have an ocean facing room and have children, you are not in luck.
The staff was most helpful. Even in high season most of them remembered us by name. Service is wonderful, although perhaps just a small tad less gracious than some of the other Balinese experiences we had, if we were to be super duper picky. The hotel is super cool and certainly has all the works in place.
The resort itself is beautifully designed, with large multi-level pool, cabanas, three restaurants (I think), and lots of rocking spaces, if you like that sort of thing. The beach is pretty and quiet, but not swimmable because of the surf. All in all we were happy with it, but imagine it is more suitable for a younger crowd without children.