The Westin Gaslamp Quarter is not actually in the Gaslamp District but two blocks away. However, that does not detract from the great location (which is the main reason I've given four stars) - adjacent to the Horton Plaza Mall, a short walk to the Gaslamp area and many other downtown attractions including Petco Park.
There's nothing truly special about the hotel - the exterior can best be described as ordinary, it has been updated but the rooms are on the smallish side, there's only one restaurant and the bar is somewhat impersonal and open to the lobby. The service is, however, excellent right from the time you pull up in your car through check in.
My beef - parking is very expensive ($36 a day) though this is generally the case in downtown San Diego.
We stayed in room 1407 which was a "deluxe city view". As noted above, it was on the smallish side but it was quite comfortable.