I love my a4. I bought it used over a year ago, and haven't had too spend TOO much money fixing it up. Of course, some things have gone wrong, but thanks to a large internet owner's community, you can easily fix many problems yourself if you are willing to learn some DIY. I have never once regretted buying it.
IMO, it is very fun to drive and never gets old. While not a rally car by any means, it has more than enough power to get you where you need much faster than you probably should get there. Overall, mine has been pretty reliable; I fixed the headlight switch myself for less than 10$, and I am getting ready to replace a leaky gasket and a stripped tie rod (both around 100$). The ride is great, the steering feels sharp, and the interior looks brilliant. Or at least it did before the previous owner smashed up the plastic console covers which cost $170 to replace.
It really doesn't get good gas mileage, which works in my favor because it means I can convince my friends with more efficient cars to drive when we are all going somewhere. The headlights are nearly useless (assuming mine are OEM), the engine can be difficult to get around and work on, and the terrible cup holders were clearly designed by people who only drank beer and were therefore not allowed to bring their beverages in cars with them. There is also an annoying whispering sound produced by the A/C (which is quite good), but you get used to it. The car is low, and because the oil pan is located at the bottom of the front of the car, you need to be careful about hitting bumps too hard.
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