iDrive is pretty terrible. It's not so much irritating to use, it's actually pretty simple. But there's so many menus and sub menus to go through to get to the dumbest crap that it makes it impossible to use while driving.
The best navi/integrated vehicle operations still have basic, frequently used operations available separately. From what I've read (I've never acutally used iDrive), you have to go through an act of Congress just to adjust the radio volume or change the climate control temp.