IMO one of the best sedans ever made. You'll get a very quick, comfortable vehicle that has just the right balance of sport/luxury ride dynamics and driver feedback...especially through the steering wheel. I've never driven a car that achieves this combination so well.
That said they can be expensive to maintain. A few quirky problems like steering column bushings and rear privacy screen gear failure.
The Roadfly forum is one of the best out there with lot's of info.
http://bimmer.roadfly.com/bmw/forums/e38/
BTW, I speak for the 8 and not the 12 (750). I also think the price is a bit high.