Nothing has ever gone wrong.
I use only high quality synthetic oil and change it every 5000 miles. I use only OEM filters and coolant. All else is by the book.
Those who have had significant problems must not maintain their cars very well. In fairness, the Audi recommended maintenance intervals (like most manufacturers) are too long. Pay attention to your Audi and use quality fuel, oil, etc., and you will be rewarded with a long lived vehicle.
In the long run, I believe higher end European cars to be superior to Japanese cars and much better than any American car. Sure, the Japanese have great quality, but most are uninspiring to drive and when they finally need repair the costs and magnitude of repair is enough so as to consider the cars nearly disposable. A good European car can be maintained well into the 300,000 mile range. And the driving experience is so much more enjoyable.
My early 90's BMW has 340,000 miles and has had no service other than normal maintenance. I expect the Audi to last as long.
I've owned dozens of Japanese and American cars since the late 60's. Switched to European cars for the last 10 years or so, due to boredom and frequent repairs.
The 1.8T, especially with the tip-tronic transmission, is quite slow from a standing start. Power is exceptional above 2500 rpm. In normal traffic, this is one of the quickest and best handling wagons I have ever driven.
The A4 has excellent highway cruising and spectacular bad weather traction and stability.
Stock, the power is more than adequate. Easily and reliably bumped to 210-240 hp with a simple computer upgrade if you desire.
Comfy and rather sporty driving position. Nice seats. Great handling.
The Audi design is very efficient. The drawback here is that the DIY home mechanic cannot easily work on this car. Timing belt / water pump change at 80k miles requires dismantling the entire font end. Do-able if you have the space and time, but certainly not the 1 hr job it is on my BMW or Chevy truck.