I travelled through Istanbul on Wednesday morning on my way from Taipei to Accra in business. The transfer time was scheduled for 9 hours 15 minutes which technically meant that I wasn't eligible for a sleep room in the lounge. With this in mind, I thought I'd give the hotel option a try even though my flight was 35 mins late landing (and took another 30 or so to get to the gate from the runway). Coming through the airport wasn't difficult and I was landside within about 20 mins even though the signage wasn't clear. There is a fast track for business class Turkish flights though there is no Turkish Airlines branding on it (it is signed as 'fast track').
To get to the hotels desk, go through immigration, the baggage hall and customs. On exiting, you need to turn right and walk past all the hotel/tour desks to the end. There, you get a ticket and speak to an agent (there's no separate queue for business class passengers). I was there before a queue formed but after, I would guess it was at least a 20 min wait to see the desk. From there, it was a long wait for the hotel confirmation and bus to the hotel.
It's unclear where you should wait after handing over your boarding pass and waiting for the confirmation but there is a seating area about 20 metres away near the long escalator. The staff come over and collect you from there when your bus is ready.
Departing the airport at 7:15, we arrived at the Renaissance Polat just after 8. Traffic on a Wednesday wasn't bad.
With my flight departing at 14:40, they wanted me to take the the 10:00 Turkish Airlines shuttle back to the airport which would have been far too little time at the hotel. There was a hotel run shuttle an hour later that was bookable for 7 euros that gave me an extra hour at the hotel. The shuttles seem to run fairly irregularly but are clearly posted. Free breakfast was offered and for the others with later departures back to the airport, a voucher for lunch was provided.
The hotel is in good shape and had a very comfortable, clean and modern room. It is in a quiet neighbourhood just south of the old airport. I got a run in on the coast path that goes for 5km starting from the foot of the hotel towards the south-west. Lots of walkers out as well and there were a few restaurants/cafes on the sea front.
All in all, I likely wouldn't do this again on a connection of less than 10 hours given the hassle getting to the hotel. 10 hours and above and its a great option.
On a side note, when I got to the lounge, the internet wasn't working and didn't work for the two hours I was there. The usual back up option of airport wifi wasn't possible since it seems that you need a Turkish SIM to receive the SMS to activate access. I missed two meetings which was annoying but the excellent food selection took the sting off a little!