Going to different zones doesn't offer any lasting variety. Its just packs of 3-5 Venatori/Bandits/Hurlocs, punctuated by an endless stream of random wildlife.
The Rifts are just pest-control too. After the first few you close in the prologue there is almost zero variety in the demons. Once you get to higher levels, then Rage and Despair demons are more common, buts its still usually just Terrors and Wraiths.
I would really like to see respawns removed or only happen if you leave the zone completely. Or be removed all together. It just cheapens all the fights, as you just end up running past most trash mobs on your way to the quest or camp you're trying to get to, since you only have a limited quantity of potions.
The trash mobs become even more tedious when you outlevel a zone even slightly (which is way to easy to do if you do even a modicum of the side quests) then you aren't even granted any experience to maybe help you actually crush the parts of the game where you're locked out of camps.