After 16 years of owning BMWs, bought an 03 MB SL500, drove it for 2 months, traded it in for my 2007 550i. No comparison, yes different car, but the 550i truly outperformed in all areas. Let's start with peace of mind with BMW's bumper to bumper warranty, smooth transmission, more than ample power (367 hp!!), luxurious interior & amenities, iDrive is not bad once you get use to it, bluetooth, nav display is wide & split screen for other features, tons of improvement from prior models, too much to list, running out of space. It's the "Ultimate Driving Machine" and nothing in its class compares!
Too many to list: keyfob, widescreen nav diplay, POWER & handling, smooth trans, ergonomic diplays, sound system, huge trunck space, sports package, zenon, power seats with low and mid lumbar, comfortable neck rest, solid and hight quality construction, and horse POWER. Oh, I already mentioned that!
Double sunroof would be awesome. Can't think of anything else.