I drove one (a coupe) before I got my M6 and was comparing it to my 6.2 C63, the 4.0 C63, M4, M6 and others.
To me it seemed to be more like an S4/S5 rather than an RS product. In particular I didn't like the drivetrain - the engine just dies after 5000rpm or so. Some other factors were the 8AT and the suspension - none of it added up to an RS and it really just wasn't that exciting. I think this video summed it up well:
If it had the 7DCT or had an engine that went a bit harder up top I think it could be a great car.
One last thing - the plastic dash is rubbish and I don't understand why people think Audi interiors are great. The full leather available on the 3 series upwards from BMW makes the entire car so much better.