Really beautiful trail that runs for 63 miles from Hinkley to Duluth. The entire thing is paved, although there are a few spots where the pavement got washed out by the floods of 2012. There was dirt/ gravel in those sections, which were no more than 200 feet in any one spot. Easily rideable with a road bike, as long as you are careful. I am assuming those spots will be repaved, as there is fresh asphalt in many sections. There are also some areas that have bumps and cracks, but it looks like they are marked for repair.
West of the park road by about a mile you cross the St Louis River, which as noted by others is spectacular. If you only do that bit, it would be worth it. The river bridge is also only about 2 miles from Carlton, so you can access it that way. There are nice bike racks (Thanks MN DNR!) if you want to lock up and walk down to the river or take photos.
East of the park road you ride along the Forebay canal/lake, which emptied in a breach and cut a 150 foot gap in Hwy 210. The trail is probably the best place to see the damage, since you are above it. They are supposed to start refilling the canal in fall 2013, but it was still empty as of Labor Day.
I didn’t go all the way to Duluth, which is 13 miles. There is a slight downhill towards Duluth, so be aware of that: You still have to ride back, and it is just a little harder going west. But being an old RR bed, the grade is very slight, unnoticeable to most people.