I own an 06 S2R, the last of the original design evolution. When I was younger, I loved the look of the monster, no other bike captured the simplicity of a naked bike. I look at the newer monsters and see the similarities to the original icon, but it is being plasticized and molded in what appears to be cheapening the design and manufacturing. To me, this is inline with all the jap bikes that produce a naked bike, they have many cheap looking parts molded to them. The original monster design stood strong from 93-08(or maybe 09), the engine choices changed and swing arm types were altered, but the overall design and execution were the same for 15 years. These older bikes (now) had way less molded parts then, as the bike truly looked like the parts bin creation it was, all surrounded by a complete trellis frame Ducati was so famous for producing.
IMO the newer generation monsters still look better than the competition, and they clearly look like they have descended from the original, but a full trellis frame without a bolt on sub frame and lots of plastic molded bits hiding areas is a huge part of the aesthetics. But, monsters are meant to be customized as the owner wishes. Again, this is all my opinion and if you are reading this and own a newer (less attractive..haha) monster, i am jealous of the new performance you have at your fingertips, but i didn't by an Italian bike for the tech.
While others claim that it is technology driven as to why the monster has changed its shape over the years, i disagree, it is more to do with the Ducati bean counters trying to extract every last penny from the most successful bike the company has ever produced. So if you tell me that i can't fit ABS, or larger catalytic, or newer tech(TFT, better headlight, adjustable suspension) like the new bikes on my 06 S2R without a full redesign of the bike, I'll call BS on you. Ducati didn't need to change the original iconic design, they wanted to make more money, so they added cheaper manufacturing methods. BTW, this all helped spawn the cheaper 1098, and help Ducati get their super-bike to more customers that wouldn't spend the money on a finicky Italian bike, so there is some good as to they cheaper manufacturing methods clearly.
in the end, Monster owners bought this bike because it is still an elegant design where less is more, even though there is more to the monster than there used to be.