It's better than the standard headunits and we're talking about a £2500 headunit here. It sounds a lot better than the Sony that was in my previous W202 and it sounds great through my current Bose setup.
Navigation is fine, POI is down to the discs and TMC works fine on the CD versions, please catch up navteq or whoever makes the discs for that!
UHI works on the older comand units as well as new, this includes phones currently in production/circulation as well as older units. I don't know anything about any faults.
I can put the original headunit back in my car if I want, just need to swap the oem parts back (fascia and frame). For some models more work is needed, others less.
As far as feature integration goes, nothing can beat comand in a car that could originally have had it installed as an option from new.