This is a great trail; in fact, all the ones in this park are awesome. Campbell's Pond, though, is a little more technical with more climbing. It's full of roots and rocks, too.
For an out and back, it is great. Most are boring on the way back, but not this one. They actually include some route diversions to make it interesting. It is really well marked, too. Although it's not as fast as K-3, you can still get up some speed. You'll need it when you hit the Kamikaze, a big dip on the way. You'll want all you can get on the Devil's Backbone...not as dangerous as it sounds, but can be great fun if you rail into it.
For better directions, look up the Killer Three Loop, which is one of three trails at Manchester State park.
http://www.singletracks.com/item.php?c=1&i=1375