Overall, Sebastian Vail was a good experience, and I think for Vail Village is one of the better choices if you go the hotel route. I will say next time we plan to stay in Lionshead as there seemed to be much more going on there for us, but not because of the Sebastian.
Upsides - Staff was incredibly friendly and always willing to help. Ski valet was fantastic - perfect space at the base of the mountain where you could relax inside, store boots, skis, etc., have a coffee pre-skiing. Bar was good for apres. Room was clean and nice. Design of hotel itself is pretty interesting and fun. Decent value compared to elsewhere in town that we have stayed.
Downsides - Room was small (deluxe king), one tiny window and no view (other than of the building next door - most of the views from what we could tell were reserved for the residences). No overhead fan, so it was hard to drown out the noise from the hallway and outside to get to sleep. Bed was not especially comfortable (duvet very light and not cozy), bathroom was very small and had some plumbing issues. Turn-down was inconsistent, some nights we got it some nights we didn't, including on nights where we had dinner reservations made through the concierge (in which case I would expect them to know we were gone).
Tip for breakfast - there is no a la carte option at Leonora, so even if you only want a few eggs and some toast, still have to pay $28/person for the buffet. Went across the street to the Four Seasons the next morning and paid far less - never would have expected that!
The one thing that irked my husband the most was the movie/tv situation - there were limited tv stations and movie channels, only the "Redbox-like" (as described to us) free rental station in the lower level for movies. The movie choices were pretty terrible - it was kind of a collection of movies that went straight to DVD. After a long day of skiing and apres, some nights all we wanted to do was lay in bed and watch a good movie and so were a little disappointed.