In a word, disappointing.
Reliability was average at best, and parts backup from Germany was poor. A combined 6 week wait for the coils and the air-con compressor took a week. Dealers were efficient, but I didn't think they tried particularly hard. I had to argue for a courtesy car when my car was immobilised with coil failure the second time and they couldn't give me a delivery date for the parts.
The TT is good to drive with punchy performance from the 225PS engine and excellent traction from the Quattro transmission, but hardly the last word in involvement. Felt more like a (very) fast Golf than a sports car. Easy to drive fast, but little reward for doing so. Takes no skill whatsoever to push to its limits which is either a good or a bad thing, depending on your point of view.
By all accounts the original "pre-recall" version (the one that was involved in the high profile accidents) was a far more rewarding car. I suppose you cannot blame Audi for playing safe against the insidious spread of the lawsuit culture.
Excellent quality interior and dramatic styling were the two areas where I thought the price was justified (and the two features that sold it to me within about 5 minutes of looking at it), but there are now so many around that even the styling doesn't really stand out any more.
Good used values. Got an excellent trade-in against a Nissan 350Z. To be honest, it doesn't have the same quality of finish inside, but it's a far better sports car.
Looks good, goes well and holds its value. Better pose value than entertainment value though, and don't expect it to be problem free just because of the Audi badge. It seems those days are long gone.