Being a Predators fan north of the border, I see a big distinction between over/underrated when it comes to locals/this board and the general talk amongst the rest of the league.
Underrated:
Klein in particular by Nashville fans, I thought he seemed like a solid player when I've seen him play and for what he's paid I would count him as a steal. But then I read these boards and am often like, "Oh man, what am I missing?" (As Cashville mentioned, this may be turning around.)
Erat by the rest of the league, his name doesn't come to mind when talking about dangerous players in the league, but whenever you play Nashville, he seems like the one to watch.
Bourque perhaps, haven't seen all that much of him, but amongst the rest of the league, he's almost an afterthought but most in Nashville I've heard from seem to think he could be a big piece of the future.
Blum by Nashville fans? I heard a lot of frustration with him as being overrated last season when my feeling was that his struggles were entirely natural for a young defenseman's growth curve.
Overrated:
Not trolling, but I wonder a bit about Rinne being a tad overrated in Nashville AND the league. Love him for sure and props to him for signing long-term without drama unlike the other big two, but for $7M/7years, I dunno, the value question starts to nag at me, and as Predatorbill pointed out, how much of that is credited to the suffocating defense? (Dan Ellis with Nashville at times looked like solid starter material.)
Wilson by Nashville fans? He seems the centre of attention either good or bad in discussions with Nashville, but I've never seen him really make much of a difference that grabs your gut and says, "Wow, this guy is taking control" the way other prospects of his stature at least have shown flashes of (Cody Hodgson formerly of Vancouver now with Buffalo, and Zack Kassian formerly of Buffalo now in Vancouver come to mind).
Maybe Ellis by the rest of the league, after his performance at times in the WJC's many whispered that he was a future Paul Coffey, and some here are surprised to hear that he hasn't earned a guaranteed spot on the Preds yet. So outside Nashville, I think Ellis doesn't have the question marks those that follow him closely do.
Beyond the individual, the offense in underrated by fans outside Nashville, the Preds still carry a reputation of dull and boring, but the stats offensively say otherwise. I'd also say that the fanbase gets plenty of props by Vancouver media due to the times Nashville has played Vancouver, but gets underrated by anything out of Toronto as "not a hockey town".