The hotel wasn't busy. If you want "action" you should probably pick the Park Lane or Trafalgar locations. We picked this location because of:
1. The proximity to the green park tube station (Piccadilly line as well as jubilee line... so you had a north/south as well as east/west tube really close)
2. The proximity to Buckingham Palace (my wife was really excited when she found out Buckingham was on the other side of the park from us... and Green Park is rather small compared to other parks in the area. She is "into" the royal family so the proximity to Buckingham was a big deal for her).
3. We could book a premium room at a lower rate than the regular 50k per night as well as get 30% of the points back with the special at the time.

The hotel bar is actually a specialty martini bar (we didn't know that until we arrived). I'm a gin drinker and have a variety of specialty gins that aren't available at normal outlets in my personal bar. Half the bottles they had I'd never heard of (needless to say I had a couple martini's each night). The bar/lounge was of decent size (not very big, but enough tables that it wasn't tiny). There were usually a half dozen to a dozen folks each evening enjoying a drink.

The front desk location is in front of the main doors with a small lounge/waiting area with a couch and a couple chairs to the side. Opposite the front lounge is the bar/lounge area. Walking through the bar/lounge area is a restaurant. Breakfast was good with plenty of options (free for gold/diamond), we thought dinner was overpriced, ate there once and didn't return of lunch or dinner. There are a variety of bars and restaurants around the corner (the concierge can point you to the area). There were business folks who stayed there as well as tourists. It's a rather small hotel, so it really isn't very busy (that could be good or bad depending on what you are looking for). As tourist we enjoyed the hotel and location. Service was outstanding. With that said next time we are in London we are going to try The Bentley in Kensington (we walked by the hotel and it looked very luxurious). We have also stayed at the Waldorf at Syon Park and I do not recommend that hotel (it is in the middle of nowhere).

We very much enjoyed our stay at the Green Park Hotel, if we had the ability to book it for such a reduced rate again, we would do it again in a heartbeat (I think it was 43k with a little over 13k back, resulting in a room at slightly under 30k points per night). If priced right (ie much less than the other Hiltons in London) this is a good hotel in a great location. It is also the smallest Hilton in the tourist area of London so keep that in mind (quite... it is really more of a boutique hotel).