An interesting question.
I'm glad they've lasted as long as they have because if I only had, say, 3 cd's to listen to I'd say they weren't my favorite band, or as I have been referring to them recently, my all time favorite band. The reason for this is that if I only had 3 cds, I don't think there'd be enough variety. They would get old.
To me, each release DT has done has been innovative, original, and fresh. Though I admit that SC and BC&SL were a little saturated in metal and a lot less proggy/innovative/fresh. Each release has had moments of beauty and grace.
Since I&W they're lyrics have always been able to reach me on an emotional level. Not many other bands I've heard have been able to do that for so many years.
Best. Band. Ever.