I am a fan of "Arrested Development" and know it's not doing so well, but it is at least *recognized* as being a good show (it has won awards, etc.) So my vote goes to "Veronica Mars". It's a great show about teens written for adults, it's much smarter than it appears, and it's managing to keep a lot of plotlines in the air without doing much ball-dropping. Plus, it's pretty and vaguely Buffyesque (except without the monsters and stuff. :)) (An LJ friend said it better than I could here: http://www.livejournal.com/users/wisteria_/470836.html ) I guess it's recognized in the sense that critics tend to like it, but it's ratings are low and it's not as talked-about as AD.
As for overrated...Hmm. I tried to watch "Joey" when it started, but I find it incredibly bland and stereotypical. And it's doing just fine ratings-wise. There is no justice in the world.