I used to love Diesel at the time when I graduated college about 2-3 years ago. It was a revelation from the Abercrombie + Fitch jeans I used to wear and I was like the first person to sport the "Wish" styled shoes on my campus (or so I would like to believe). I got soo many compliments on those shoes it was not even funny. Even when I thought the brand was hot I knew it was overpriced, and I still have two pairs of Zathans that I wear as my "beat" jeans so I have to say the quality is pretty good.
I won't buy anything from the brand anymore because I think it killed its own uniqueness by too much mass marketing (and the fakes that are flooding eBay and Asia). You see the most unfashionable people walking around in Diesel shoes nowadays, you see clearance racks full of Diesel shoes, which makes them lose most of their appeal to me. If you don't believe me, check out the LOADS of Diesel stuff on YOOX, I think it's hard for Diesel to sell their stuff at their desired retail value nowadays.
Anyways to me it's just another nameless and souless "designer" brand and I will put them in comparison with Abercrombie, Energie, Tommy Hilfiger, etc. They'll always be good for basics (jeans, tees, occasional jacket) but I certainly am not having any higher expectations for their stuff.
just my opinion, cheers!