Is there anything similar to Oscuro's Oblivion Overhaul that makes monster difficulty more realistic? That Oblivion mod did so mainly by removing monster level scaling with player level. Monsters were given a static difficulty based on their type and some other factors. For example, all wolves were easier than all trolls. I enjoyed the challenge of being aware of the type of enemies I was facing and needing to test whether they were too strong. In the built-in system, it's generally possible to kill almost anything starting at early levels, and there is no sense of excitement at being able to go somewhere that had previously been restricted.
I did spend 20 minutes or so on Google trying to find something like this, but couldn't come up with anything.