For me, I stopped liking the YZF-R1 after 2003. That was the last model that did anything for me. It was light, fast, very torquey, and handled well. The only problem with it was that it was always in the shadows because of Suzuki's dominating literbike.
I felt the R1 went to shit in 04 when they it gained all sorts of pounds and lost all sorts of "character defining" low end torque. The then, trend following, underseat exhaust didn't win me over either.
You really need to ride the older R1's to understand what I'm talking about here. The newer bikes weren't bad buy any means but when you do a direct comparison to the older versions, it's clear that alot is lost. We're talking streetbike here.