Fairly solid, but below Westin class
I've stayed in The Westin Seattle several times across last 4 years. In my opinion it offers a standard, mid-level hotel experience, unfortunately below what I've come to expect from Westin and Starwood brand. 
My last stay (July 2012) featured a high-floor room (SPG preferred floor). Room had an impressive view of the downtown Seattle (45th floor) but it also meant I spent significant time waiting for one of those 4 elevators to be available for usage. 
Room was tidy, well furnished, with very comfortable bed. Sleeping was particularty pleasant due due to low noise (high floor) and surprisingly quiet air conditioning device.
Hotel's staff was also very professional and helpful, with one major issue. I ordered a package from Amazon which they managed to misplace in the warehouse. After 4 days of looking, they were still unable to recover the package. Also, while being very friendly, they did not really made a real effort to find the package. Hopefully they'll be more successful next week (business center is apparently closed for weekend so they cannot look for the package - amazing).
Aside for that, solid hotel, good stay, slightly overpriced when compared with competition.