Why someone would view a newer MB as "junk" I don't know, but they certianly aren't being very objective. I own a w123, and while its a nice car, even considered "legendary" by some, it certianly isn't the greatest thing on the road. I can think of lots of drawbacks (horrible seats, mediocre HVAC, lots of cabin noise, poor handling, miserable gearing for highway cruising, etc.) Sure, the w123 is a great car FOR THE ERA, but its drawbacks are why the company improves the design and markets newer, better cars.
That said - I have read a few places that the S-class cars starting in '93 are some of the best Mercedes made (as far as interior material quality, fit and finish, ride quality, etc.). I believe they are the w140 series? Possibly a little biased, but one such article was in Mercedes Enthusiast magazine over the summer. Sure, they frequently blow a/c evaporators and are more technically complicated, but every car will have its problems.