I can't enjoy games without exp/level up/currency systems for prolonged periods of time because I don't feel "rewarded" for my "effort".
If you don't get some items/experience/money or any other tangible long term reward from killing an enemy I don't feel incentive to even kill it. Especially if it takes resource like bullets.
Best case scenario is that you spend some bullets and enemy drops some bullets, hopefully more than you have spent, but that's about it.
It all started in later 90s with SOTN and Diablo 1 where I felt unadulterated joy of getting more powerful just by killing regular enemies, getting stronger equipment and new abilities through that, and not just through chronological/geographical progress like in most action games prior that era.
I realized this recently when I tried playing some classics that I missed like Half-Life or Doom. I just don't feel encouragement in keeping playing.
I know there is progression where you find stronger weapons and what not, but just killing each single enemy doesn't give you shit, except for bullets that you've already spent.
So the question is - how do I cure myself from this skinnerbox cancer addiction to exp? Especially with single player games perpetuating it this days, as you have exp in everything - cuhrazee games, shooters, even platformers.