I'm gonna be all hipster and cool.
Underrated: Mach Tower
This is a ride everyone just loves to hate, mainly because of its dud status, but when it's running right, it delivers a pretty awesome ride. Sure this ride isn't as tall or as intense as Drop Zone or have the (rather pointless) special effects running, plus the horribly uncomfortable seats, but it still gives awesome views, a pretty thrilling drop, and waiting at the top (even in observation mode) is relatively nerve-racking.
Overrated: Griffon
It's been said before a few times now. Might as well not be so redundant.
Overrated: Skyride
This isn't really about the ride itself, it's more about the lines this thing gets. It's a pretty common complaint I hear that this ride can have some pretty long waits. If you want to get a nice view and the lines aren't too bad, I'd highly recommend it. If the lines are bad, you might as well walk. You'll still get to take in the atmosphere, just from the ground.
Neutral: Train
A nice, relaxing way to get around the park, plus good views of some of the coasters, rides, and even some backstage areas. Still incredibly popular with just about everyone, but stations are hard to find for newcomers and sorta spread apart a bit.