Depends on class of travel. Here is my experience of QR lounges at Doha.

1. Unless you are flying First, no access to Al-Safwa First.
2. Business class tickets on QR and OneWorld flights get access to Al-Mourjan Business. Access is via the escalator with QR guards/staff at the bottom.
3. OneWorld status passengers not in Business or First are shunted off to the distinctly inferior Oryx Lounge which I think any passenger can pay for access as well.

Do look out for the giant cuddly bear in the main atrium.