When you have XP per kill but you do not have respawning enemies the game the game usually becomes a sort-of-milestone-kind-of game or Murderhobo paradise.
That said, I´m ok with no respawning enemies, I´m not a fan of grind-until-you-puke games.
I agree. D:OS2 had extreme level scaling, no respawns and killing things gave exp, plus you could not return to a former map.
This setup strongly encouraged players to kill everything before moving to the next area.
Prof. Dr. Dr. Mad S. Tist 
