Stroll along the Doha Corniche and watch the sailboats. Very, very pleasant of an evening. The suq is okay, but not brilliant, the gold suq is sort of so-so -- certainly not up to the standards of Manama, Dubai, Riyadh, or Muscat.
The Corniche in Doha is one of my favorite places in Qatar, and there always lots of people. It's nice for a walk and a talk with friends :)
At sunrise is the time to be there, it's simply breathtaking!