Hmmm... I guess I just buy what I like for the most part.
Sometimes I'll go out of my way and research one particular model and try to obtain "special" variants- like first production runs, or one-off handle materials, stuff like that. I suppose that's the collector in me.
I've read a lot of commentaries bashing so called "me-too knives", yet I don't really subscribe to that notion. If I like one model, and so do 5000 other knife nuts, well, then that doesn't make the knife any less desirable- it just speaks volumes as to what good taste we all have in knives!
As for one that didn't live up to the hype, two stick out in my mind. My first Cold Steel Voyager, long before I was aware of any other companies- I bought the CS hype, and was severely disappointed by the el cheapo Fisher Price feel. The other was a Boker/Brend. These received a lot praise when they were first introduced, but the example I got was a total POS. Poor build quality, cheesy lock and wobbly as all hell.
Live and learn though. I just buy the stuff that "does it" for me.
The only Cold Steel knife that I bought (actually traded for it) that I was even just a little disapointed with is my Mini-Tanto, and the disapointment was due to it being a little smaller than I had thought it would be. But still, it IS a "cute" little well-made knife...