nice drive, gas mileage not great. highway max you will get is 24, city average would be like 17-20 depending on how conservative you drive.
other than that, the car is really nice. it has a nice onboard computer that calculates everything for you. alot of little functions that make your life easier. back seats are pretty comfy but give you a small feeling since the windows are basically nonexistent. the ride is VERY nice though, something your wife might like. another good thing is that mercedes benz is offering a 3000 rebate on the vehicle, so you can get one very cheap. just dont expect to sell it easy =p
yeah overall, its a great quality vehicle. i had 0 problems with it, and as always mercedes servicing is great. the supercharger is also nice in case you want to have a little fun with it from time to time. sound system isnt as good as a msp of course, but it is decent. people say its "the worst mercedes", but you are getting alot more than that title gives justice to.
it all depends on what your wife wants though.