Keeping in mind that beyond the first $50 or so, pretty much everything we discuss in this place is highly subjective, but the most over-hyped to me would probably have to be either of these:
CRK Sebenza
I'll say it. I'm not claiming it's a bad knife, or not worth the money. The one I bought was very nice, and the fit and finish was as fabulous as I expected. It was just a disappointment because there is always so much hype about the Sebenza being the gold standard in production folders.
It wasn't superior in ergos to my work horse knives, and it wasn't superior in appearance to my pretty knives. I found it sort of a really, really nice knife that didn't do either thing well enough to make me want to keep it for anything other than style points.
Spyderco Paramilitary 2
This is another knife that I really like, but I think is over-hyped here. It's a very nice knife, but I couldn't replace my BM 940 or BM 710 with it. The 940 packs as much blade in a significantly smaller, lighter package. The 710 packs more blade into about the same amount of pocket space. It's a nice knife, but the amount of love it gets here is silly.
. . . again though, to be clear, I'm not claiming either the Sebenza or PM2 isn't a great knife, or saying that either isn't worth the money. Just that, IMO, both get way too much love hereabouts, compared to the reality when I'm holding them in my hand.