Have had my Z4 for a week now and even with trying to take the car from my wife and constantly arguing about whose car is it, it's still worth every second of owning. After owning my first BMW I don't believe I could ever own another brand.
Everything from the sleek aerodynamic design to the awesome exhaust sound when at about 4000 rpms or higher. The quality of the Z4 is untouchable.
The seatbelt cuts into your neck leaving a mark on it. I try bringing the belt down towards my chest but it keeps creeping up. Other than that.. come on, it's a bmw.