The standard sound system isn't that great, but you have to appreciate BMW for making subwoofers standard and earlier models came with an amp as well. That paves the way for a better system because the only upgrade you really need is a set of decent speakers.

The real culprit is the muddy, cheap-quality speakers. When the front speaker died for no apparent reason, I replaced them with a set of Alpine 4" ones that were on clearance and fairly inexpensive. Now, the sound quailty is much brighter and crisper, and the speakers only cost $50!