BTW, I should add that the damage returned is 60-100% of the corpse's life, of which that return is 50% fire and 50% physical damage. That should be more clear.
Monsters in Hell have a lot of life (which is why CE is now so deadly, I think), but a few CEs clear them easily in solo or small games. Requires more CEs in larger games, but as long as you have mana and some fcr, this isn't too much of a problem. Adding more points into it gives it a rather large explosion radius (I think my necro has 12.5 yards or so with Level 30 CE), so you can have several quick overlapping explosions which is deadly against enemies. The larger the pack, the larger the life of the opponents, the bigger the CE chain you can get going and overall damage. CE usually kills monsters faster in Hell than my skellies can.