I actually bought the first three trades of the current Sonic The Hedgehog run recently as i'm kind of on a "support the heck out of Archie" kick after falling in love with the reboot of their line last summer, and yea as far as comics based on 90's Video Games icons goes it's a pretty fun read. Nice to see them use characters from the old sonic cartoons on top of characters from the games. I also got the first Worlds Unite book, but haven't read it yet as from what I understand it happens at a future point as the STH trades have only collected up to like issue #263 and Worlds Unite happens in the mid 270's. But yea, fun series.
Lets see, what else... I would say Sandman Mystery Theatre is abit underrated, it's a solid series but I haven't seen much hype for the current reprints of the series in bigger volumes.
As for overrated, I love Grant Morrison, but I think his run on Batman is kind of overrated. It's not bad mind you, but I personally find it some of his weaker work.