The Reservoir Lounge is one of the first jazz bars I had ever been to. It's down below the main floor and quite dark inside. If you are planning on eating, I would not go to the Reservoir Lounge. The pizza I got was tasteless and soggy and not worth the money at all. They don't offer much on the menu other than some salad and pizza.
For those we came after dinner, cover was $10. The staff wasn't overly friendly or helpful, but still nice. It's a very intimate, crowded space with small tables and limited seating. If you don't get here early, you won't find seats. The drinks are okay. The live band was energetic and fun. Heck, who doesn't enjoy a good live band?
I would go back, but I'd eat dinner elsewhere and come in early for a good seat.