We had a fun first night in Cusco at El Truco. I really enjoyed the two different bands and the dancers. The place has a nice, if not a little touristy atmosphere. My dish was quite average (spicy chicken, which wasn't spicy at all), though others in my group really enjoyed their meals. I was really impressed at the speed that the waiters would come down the stairs with full trays in their arms.
I recommend it!