The biggest problems:

 

Transmission - Terrible engagement from a stop.  Kind of like driving an old car with a clutch that has a very skinny friction point. Hard to start smoothly. However, in the SLS, your hard to start smooothly issue is compounded by a 570 hp motor!   So you wind up blasting off like an @$$hole from traffic lights and stop signs, without necessarily flooring it at all, it just does not engage and then it explodes.  Big / huge problem.  I did get better at fluttering the throttle over time, but it went from terrible to modestly manageable.  A honda civic is more predictible off the line.  It is a dual clutch, of the same type found in Ferraris, but MB has slowed it down for some reason and it does not engage gears quickly in manual.  I found this really annoying.    There are 4 teansmission programs, C, S, S+, and manual.  The starting issues are less bad in S+, however that mode tries to redline the engine under even modest acceleration attempts.   So I basically never found a transmission mode that I liked. Smiley                

Width - the SLS is exceptionally wide.  I have never seen a car other than a Rolls Royce so wide.  It basically does not fit on narrower side streets.   

Flashiness - This is a personal taste issue.  I have never bought a Ferrari / Lambo or other exotica because of the attention factor.  Myy old 997 C4S got no attention at all, one of the merits of Porsche's obviously.  I had thought that a silver Mrec that resembled an SL would not be particularly noticeable.  Big mistake - it got a ton of attention and much of it the not so nice kind.  Other people will likely have a different experience, but I don't desire conversations about my vehicle choice or occupation or other things when I get a morning coffee.

Practicality - there isn't any.  This is similarly a personal choice issue.  But short of commuting to work mostly by highway (not my situation) and Sunday drives, it is not a serious option for much of anything.

To be clear- - the car has some significant merits.  I thought the suspension setup and ability to place the car were excellent.  You sit way the hell back - for a guy coming out of a 911 it is a particularly jarring change.  But you do figure it out, and it is a distinctive ride.  The power is explosive, and the noise cannot be topped.   The cockpit is very cool.  On the highway, in the mountains (only on a warm dry day), I would describe it in orgasmic terms. 

I am going to try a new SL63 on for size - 95% of the capabilities, maybe more accelerative, does not have the transmission issue, might have more power at altitude anyway, and vastly more practical and non-attention grabbing.  If that fails, I am definitely going back to a 911.