Think I heard that thay are a bit unstable, i.e. more liable to topple over (cornering too fast?) than other cars. This may have been rectified since. Friend of mine had one for a few months one time and didn't think much of it.
Original issue was the car failed the Moose test in Scandanavia. (A quick swerve resulted in a roll). All cars were recalled and fitted with a stablisation system to overcome this weakness.
Not aware of any other issues - I sure being of german build it's very reliable. Only problem is that the engine is under the body so access is difficult.
Awkward driving position - pedals slightly to the side.
Main dealer servicing costs astronomical.
Very overpriced for what you're getting and resale value not as good as other German cars - but hopefully this to your benefit if you're buying 2nd hand.