The business class lounge and the first class lounge are both located in the new Premium terminal. I used the business class lounge twice in December while in transit.
As mentioned by Qatar340, the terminal is exclusive and passengers are greeted by QR
personnel directly after entering the terminal. After a quick security check, one passes through the duty free shopping and goes up an escalator (with a waterfall surrounding) up to the lounge level.
At peak hours (23.00 - 02.00h) the business lounge was very full, and it was difficult to find a seat, but it could also have been a result of the Asian Games taking place. The business lounge has a restaurant style dining area, and the QR
personnel come around to take orders for drinks(!) and announce the boarding of flights. The spa is only available to first class passengers, but the bathrooms in the business lounge are large and have large showers.
All in all, QR
inflight service and ground service are remarkable!