We stayed at the Lancaster Gate a couple of years ago, booking it through londonnights.com. The hotel is on the back of a little square behind a church at Lancaster Gate, just behind Bayswater Road. It's only a block and a bit from the Lancaster Gate tube station, a couple of blocks from Paddington station and only a little further from Queensway and Bayswater stations, both definitely walkable in less than 10 minutes. Busses run along Bayswater road and Hyde Park is right across the road. You can walk across the park to the Knightsbridge museums in 10 minutes.
The room was large, (we had a double) and they have family suites as well as singles and twins. There is a little fridge in the room, very useful for having milk and snacks. The bathroom was a decent size with tub and shower and heated towel racks. Rooms are air conditioned.
Continental breakfast was included in the price, eaten in the small breakfast room in the basement. There is a lift in the hotel but there might also be a few steps to the room as there was with ours which was off the ground floor.
The little square was quiet. Beds were not *really* comfy but not too bad either. I'd definitely stay there again as i like the area for transportation.