It sounds louder than stock almost everywhere. Boomy loud on initial startup, then when the mixture settles in it's not bad at all. The big tradeoff with aftermarket exausts, IMHO, is usability with the GF in the car vs. awesome sound. I have the cat-back only.
With the AA Exhaust, it's fine as long as you keep things above 2100 rpm. Below that, it's boomy; especially with the top down. I've learned to adjust to it: I don't lug it around town any more. The motor is probably happier for this adjustment, as well.
The AA is simply stunning from 2100 rpm up. It's the way this motor was meant to breathe - and sound. My E93 was a compromise for what I really wanted - an F355 - but I couldn't fit in the darned thing (and of course they're crazy $$$). With this exhaust, I'm very happy with the compromise. It isn't exactly Ferriari-like, but it's a really good sound that's not too far off.
I have a rattle apparently caused by the exhaust touching the rear X-brace that's in the E93. It's only occasional, but I want to work with it to get it to go away. In fairness I haven't asked AA for advice on that yet.
Never leave a car completely stock!