Firstly, this is an airport hotel. If you need fast in and out of the airport, this is a very good spot. We went here knowing what to expect. Rooms are big and clean, bathroom is clean and the water pressure is amazing. The hotel is huge, the staff is amazing and it is next door to Heathrow.
Cons are the limited dining option, they have a place where you can get some coffee/juice and ice cream and a restaurant that is in this massive room. I guess they do buffets here twice a week.
Be also aware that this is one of those hotels where buses of tourist gets dropped off and other packaged/school outings and trips stay. Do not be surprised when you arrive that there are 50-100 people walking around the lobby.
There is an underground stop across the street and it is a good spot to stay when you are about to fly off with an early flight, this is not where to stay if you want to explore London.