Hey Scott,
Actually it's NATS standard policy not to give feedback, though a few people here have managed to get some by badgering them a bit, but its probably too late for you now. I guess it's not too big an issue if you have a fairly decent idea where you went wrong though.
Apparently the format of stages 2 and 3 has changed over the past 12 months, but I've no experience of what it was like previously so can't tell you how it now differs. There are some fairly good descriptions of each stage if you read back through the thread though.
I recently did a tower visit at Southampton, if you'd like then PM me and I can send you the contact details I have. At the minute NATS seem not to be encouraging tower visits until after stage 2, at which point most people seem to organise them by getting the contact details for the towers they want to visit via HR. I believe stage 3 involves a tour of Swanwick (can someone who has done it please correct me if I'm wrong) so you get to have a look at an area centre at that stage.