First of all, something about Fallout 3 I never really liked: It made post-apocalyptic wastelands seem easy. They made the wasteland seem like a happy-go-lucky sandbox. Once you get to level 25 or something, you are able to completely overpower nearly every enemy by then.
I like the additions they've made already, with the hardcoe mode: dehydration, stimpaks, and doctor bags, the gameplay seems pretty awesome. But, I believe that hardcoe should be well, hardcoe. And by hardcoe, I mean unbelievably difficult, but doable. Because that's what wastelands are about, right? Survival, not pwnage. Every single encounter with a mutated beast should be a grueling life/death thing, with more interactivity with enemies. Also, limping, and eventually crawling when limbs are broken would be cool. Mutated limbs should grow, and either aid or attack you. And you'd have to like, saw the mutant limbs off, which would also be sweet.
If you have any other suggestions or ideas, post here! Thanks