The Hilton Olympia is an old English style hotel and is showing its age. My wife and I stayed at the hotel three times in our first few weeks in London. The rooms are dated, small and cramped. The furniture was worn. On two of my three stays, even though I asked for a non-smoking room, the room I received smelled smoky. The service at the front desk was adequate and there were people to help with bags. For frequent stayers at Hilton, the front desk staff did not seem up-to-date with Hilton policies.
The breakfast buffet was expansive having English, Continental and Japanese choice. The food looked presentable, although they tended to run out of things if you came down later in the morning. My wife and I enjoyed a late night club sandwich and chips in the bar, which they made for us even though the kitchen had closed.
The hotel is close to many attractions such as Kensington High Street and Hyde Park. There is a extension tube station next door (infrequent service), or you can enjoy a 10 minute walk to the station in Earl''s Court. Although I am not positive, I believe the express train to Gatwick leaves at the train station next door. To go to Heathrow, I recommend using the mini-cab stand that you find by turning left out the hotel door. The hotel is near the A4 which goes right to Heathrow. Make a reservation the night before.
This was not my favorite hotel, but it is a Hilton and well situated. It also tends to be less than some of the other American chain hotels. If you get a good rate and want to stay at a Hilton, this is a reasonable choice.