I've been in the nightclub portion of The Fly once; same issues as every other club. Cramped, dark, loud. If you're into that, go for it. The real attraction is the cocktails downstairs - these people are magicians when it comes to making drinks that don't feel alcoholic in the slightest. The prices aren't the Queen's SU, but you'll save more money in here than Limelight.
A lot of my friends smoke; and since I hate being left alone, we tend to stay outdoors. Like Laverys, The Fly has a heated smoking area with lamps and chairs arguably more comfortable than what's inside. Seriously good for a night out.