Deadalready, I'm using a mod called franseca's that adds a lot of realism to the game and extra items and creatures. Various realisms from economy to weapon properties to plant regrowth to leveling.
One thing it changes (and most changes are modular meaning you can do them or not) is to make you level slower (1 separate package) and make 12 skill increases a level up rather than 10.
The first thing makes it so you can actually have some experiences at each level rather than racing through.
The second means you have 20% more skill points for a creature at your level. It also means more attributes get built up by more levels gained in each attribute skill.
The game is still challenging. For example there is a chance of a randomly harder than level fight. You can always run away and the good thing is that the treasure of that harder fight is correspondingly leveled up
Theres more variety in apponents. At high level instead of 50% chance of monster X and 50% monster Y it adds smaller chances of weaker monsters in greater number.
Another example (and this is a huge and very FUN mod) each enemy is given a combat style so that each wolf does not behave exactly the same (or bandit or goblin). More variety.
Check the sticky with mods and look for fransecas. Its hosted at file planet.
Personally I think bethesda should hire her. She made the game much better.