To me, 2e, 3e, 4e, and 5e are not compatible to each other (and therefore IMO should be called something other than Dungeons & Dragons). 2e and it's antecedents, 3e, 3.5 and the 3e 3pps, 4e and Essentials, and 5e, 5.5 and the 5e 3pps are all compatible enough with each other in their group to...