My wife and I did this route (more or less--we felt free to stray from the route in Wisconsin), went from Grand Rapids, MI north, took the ferry across the lake at Ludington, and went around the top and back down--a great time!
As was mentioned, the tunnel of trees is wonderful. In general, the 40-50 miles around Macinaw were the most scenic. The UP is also nice--Highway 2 has a nice wide shoulder but lots of traffic. Our regret is that we didn't leave ourselves a little more time to venture off Highway 2--I guess there's some nice things up there that we missed (can't remember the names right now). Also make sure you've got the tools you need--no shops between Macinaw and Escanaba (and the one on Macinaw Island really doesn't have what's needed to fix road bikes). Also remember bug spray and even one of those little misquito nets that you can put over your head for the UP! We stayed at a place called "Flowing Wells" National Forest campground and thought we were going be eaten alive! I've never experienced anything like it.
As for camping, we really enjoyed Nicolet National Forest in Wisconsin ($7 for a night of beautiful camping!). Another good thing to know is that all state parks in Michigan have a policy that they will accept cyclists at any time (which is good, they're usually full).
Overall, it was a great first tour. Mostly flat, with some longer, gentler hills in the Central LP and in Wisconsin as well. If you have time for it (and depending on your route), I'm told you may also want to spend a few days in Door County in Wisconsin (supposed to be wonderful biking!).