When the body of the flashlight gets hot, its a good sign that its drawing heat away from the LED module which is a good thing.
Its not just the R2 module, The Q5 module also gets similarly hot if run for the same amount of time.
If you reckon the heat stories about the R2 & Q5 are bad, you should check out the threads about the new SSC-P7 lights! After 15-20mins, the light gets hot enough to cause blisters on your skin!