As good as an airport hotel in the UK gets.
Stayed one night in between flights. We had the runway view superior room with a queen bed. Rooms are on the smaller side, but manageable. Bathrooms are pretty barebones but very clean (sink was surprisingly tiny, no bathtub). Bed was very comfortable. You barely hear the air traffic. But if you have noisy neighbours, that could be a problem. Staff were pretty prompt. Room service was quick but the menu was very limited. Asked for a porter to help take our luggage down, and he promptly showed up in 15 minutes (as he had said he would). TV will be a disappointment for most international travellers: a whole bunch of British channels that appear to simulataneously broadcast the same programs. All that said, dont go for any "five-star" hotel options around Heathrow. "Four-star" options are far better value for money.