I'm firmly in the "to each his own" camp ... but in the spirit of the discussion:
Overrated- Anything with Latakia in it. I very rarely find myself in the mood for it.
Underrated- PA and CH seem to catch a lot of undeserved hate in my opinion. I'm also I also don't hear much chatter on the forums about Blackwoods Flake, which is probably my favorite of McClelland's offerings.