the reviews up thread are spot on and I can only add the following points from a stay for one night last week (during the week):

Driving to the hotel:

The way is quite well sign posted on the way to the South Terminal but only once you head in that direction.

There is a 10 minute strictly enforced drop off zone in front of the hotel which is very convenient to drop friends or family off but not enough time to actually get luggage out, check-in and take bags to the rooms and then come back and move the car. They use a video camera to come out and take registration numbers of the cars and do so regularly and tickets are sent electronically from what I read. (I did stay longer than 10 minutes before moving so will see if I get a ticket or not and report back)...I may have been just lucky enough but we'll see.

There is a Hilton car park just after the drop off zone but it was full so I parked in the short stay car park attached to the terminal and this was convenient due to the hotel being connected to that car park but not inexpensive at something like £ 7 / hour IIRC for at least the first hour...

I found the hotel was sign posted quite well from the car park lifts personally and the walkway wide and nicer than the Heathrow T4 walkway (and also no where near as long as the Heathrow T4 walkway). It was around 200-300 meters in length and is straight so you can see the end (where it comes out at the Costa coffee shop and then the main atrium lobby of the hotel as mentioned).

Check - In:

There are two desks for HHonors Diamond (and I guess gold?) members which were both manned and this cut the queue time considerably as the hotel was quite busy with several people deep waiting for the normal queues. I didn't check in online as no upgrade so waited and was upgraded to the new exec rooms in the newer building at check in by the front desk. ^ Pictures and description as above by lifetimeblue.

It is truly a long walk to the room once out of the elevator to the new building (longer than the connecting tunnel from the car park to the hotel IMO.)

Exec Lounge:

anyone can enter but there is a lounge angel there to check eligibility.

Bar in Lobby:

We had a drink before leaving with relatives and it was a bit pricey but service was good and quick. Plenty of seating with some behind the bar in addition to the seating area in front of the bar.

Seemed reasonable enough, I'd return and a good full service place for Gold or Diamonds to stay and get some benefits over the Hampton in the North Terminal.

hope this helps those wondering whether to stay at the Hilton or the Hampton here. Both are good, for those with no status I'd go to the Hampton as breakfast is included and for those with status I'd stay at the Hilton.\