The Icehouse Trail itself is six miles of almost non-stop downhill, descending 2000 vertical feet. There are occasional very short gentle climbs to keep you honest. Intermittent pumice boulders situated in the trail surface would be a pain to stumble on. The final 1/3-mile plunges off the mesa is more rugged and a little steep at times.
Those who want to earn their vertical -- or who don't have a shuttle -- can run up Cottonwood Road for an 18-mile loop (uff!) or you can run this as an out-and-back.
It might be wise to use the Trail Run Project mobile app
on this one. The start is very difficult to find, and there are no signs above the Broken Mesa/Icehouse trail junction. It is also very easy to lose the trail in the upper sections. Beware that this appears to be a user-created trail, and mostly goes directly down the fall line, which means that it has become a watercourse and is now (in 2016) a rutted rocky experience. This trail would be greatly improved and more sustainable with reroutes off the fall line, which would be a huge project.