Most of my information is just from exploring the area myself. I haven't been just a ton (about 5 times), just enough to know there is still a lot of places left to explore (kind of like Big Bend). I've got TOPO! for New Mexico and use this as a way to discover new places. Also there a a few hikes in the area written up in guides and the Lincoln's website has a little info. The Guadalupe Rander District map is also useful for roads and land ownership. What follows is a list of my trips:
1. Camp Wilderness Ridge Trail- Starts off as a dirt road and progressively becomes rougher until transitioning to single track. Spectacular views into North McKittrick Canyon and GMNP. Saw no one that weekend.
2. Devil's Den Canyon- Starts off as a dirt road and transitions into single track. Descends into Devil's Den. Has a spring which was flowing in August during an "average" rainfall summer. Nice views, interesting canyon. Tons of maple. Would be pretty in the fall. Saw 1 truck parked on the side of the road.
3. Big Canyon Ridge- Follows a Jeep road. Spectacular views. See
http://griffisfamilyoutdoors.blogspot.com/2006/12/1117-192006-guadalupe-mountains-nm.html Didn't see anyone.
4. Last Chance Canyon- Did a loop up Sitting Bull Canyon past the falls, up over a ridge and down into White Oak Canyon descended into Last Chance Canyon and explored along the creek . The upper reaches of Last Chance are beautiful. Didn't see a soul.
5. Sitting Bull Trail- Started up on NM 137 and descended the trail into Sitting Bull Canyon, along the creek and down past the falls. Prior to descending into Sitting Bull Canyon the trail just follows a bulldozed track through the PJ, but is very pretty after descending into the canyon. Saw 2 other people out backpacking.
This is my experience so far in the area. There are a lot of unpublicized areas as well I have yet to explore. I hope to make it out a few times this year. I avoid the area in the spring due to winds and mule deer season in the fall.