Think about it, there are lots of good ideas in those mods. As an Oblivion player, I have installed tons of mods that completely changed the gameplay for me.
These made it...Better. Oblivion was the base, the mods made the game be the best game ever. I will explain it a bit, cause I′m not native english speaker, so forgive me:
For example:
In vanilla, conjurations were so simple, you select the type of creature/humanoid you want, you cast the spell...Voilá.
In my modded Oblivion, you can summon every creature you want(Once you have bought the spell) BUT at lower levels the spell will probably fail,causing the creature to attack you. Also, you can summon more thank one creature...
This has been only an example. And note ideas are not mine, I just only want Bethesda to take into account moders′s ideas.
Thank you.