I think the enemy re-spawns just slightly too quickly. I get the that lots of players are moving through any location at any given time and everybody wants something to shoot at, so in that sense it's good. However, I noticed it with the Captain and couple Dregs at the entrance to the radar building during Restoration. I picked them off at a distance and by the time I ran to the door they were back. This could pose a problem with ammo supply at other crucial points in the game.