I would actually recommend going up the Faisaliah tower - you get a nice view of the city from there too, including its nicest landmark, the Kingdom Tower. Obviously you don't see that if you're in it!

There are plenty of ok restaurants. Al-Reef Al-Lubnani comes well recommended. "Good" for restaurants in Riyadh is pretty relative, unfortunately.

The city does come alive in the evening, though. Take a wander down Tahlia St. Long sleeves and trousers (not shorts) highly recommended.

You could even try to see one of the Riyadh football teams playing, if timings match up.

Are you going during the Saudi workweek (Sat-Wed) or over the weekend?