I was there with a friend of mine in 2001.  We took the train in to Redhead Lake (Nemo River) and flew out off of Granite Lake.  The isolation was exceptional, and getting dropped off on a train and having it pull away was pretty cool.  I have seen that most people get off at Allanwater Bridge, but I would certainly recommend the stop at redhead lake a little sooner.  We did not see a soul for 7 days, until we paddled within 1/2 mile of a fly-in fish joint on Brennan Lake (which is a sizable like).  Otherwise, that was the only folks we saw the entire time.  We went in early September.  Wildlife was sparse, but fishing was excellent, bugs were non-existent.  Nemo River wasn't so much river as stream connecting a chain of likes, so there was no real whitewater, just a number of small portages (many of which we pulled the boat through) and a couple of long ones.  Snake Lake was a great place to spend 2 days.  Sand beach, nice campsite on SE shore and great fishing (nice mix of northerns and walleye).  The portage into Brennan Lake was a pain in the ass, mostly because there was not supposed to be a portage, but there was so much downed timber we got out of the boat and pulled it through logs for about 30 minutes.  Brennan Falls (upper and Lower are quite impressive.  We went through the upper in an empty canoe and swamped it on a big haystack at the bottom.  Cold day for a swim, but amusing nonetheless.  I can't imagine doing anything but walking around the lower falls.  There is a lot of water moving out of that lake.

The Beaver picked us up in the middle of Granite Lake.  It was cool flying out.  Expensive (about $150 per head) but very cool, and a great way to end a trip.  But the train in is very cheap and it is a neat way to start your trip.

My $0.02 worth.