The most important thing to be aware is that they are expensive to maintain.
BMW's are expensive to maintain. Everything on them seems to cost more than a typical American made car. They must be taken to the dealership for service and maintenance versus taking them to your local mechanic. Insuring them cost a bit more than most cars do. However, they are a dream to drive. The engineering makes you feel very safe even in bad weather conditions. They last forever and if properly maintained will become a collector's item.