Jay Bouwmeester was hyped a lot as a 16-year-old. A lot. However he faded in his draft year, and the hopes weren't as high for him as the draft rolled around. I remember 2002 very well, since I was working at a major website and posted a lot of draft stuff for them. I remember being surprised at how fast Rick Nash came up in the rankings as he emerged in his draft year. In the end, the Columbus scouts made the right call there.
I go back a long, long way. Prior to your era (post-Bouwmeester), the most hyped defensemen in draft history have been Denis Potvin (1973), Barry Beck (1977), Scott Niedermayer (1991), Chris Pronger (1993), Ed Jovanovski (1994), and Bryan Berard (1995).
I did a lot of research a couple of these guys.
Potvin
Beck
Personally, I think Pronger was the most-hyped defenseman from this pre-1999 period. People were talking about his dominance at a very young age. Potvin is also up there in terms of pre-draft hype, but the draft didn't get as much attention back then, and players were drafted at age 20.