Enchanting and Smithing --> these two when mastered become too powerfull, i think everybody agree. Anyone who wants the game to be challenging (even in master difficulty) need to avoid leveling these skills. It would do no harm to nerf them a little.
Sneaking --> I think a little nerf would be welcome too. I use it a lot, its very effective to my needs and i have only 1 perk invested in it. To people who like being a thief/rogue, it's more interesting when you HAVE TO put more points in sneak skills to become a better thief/rogue/assassin, whatever.
Magic --> I personally think the destruction fire damage is fine, i cant say the same about ice/lighting damage. A lot of people think that the damage is too low overall. I'd like to see more studying needed to be a good mage, i mean that creatures should have more specific resistances/immunities, i can beat almost everything with fire - personally, i didnt find anything that i couldnt beat with fire, it would be cool if i were supposed to try cold/thunder/fire to find the best kind of magic i sould cast against my enemies. The illusion effects could be quicker too, only one cast usually is enough in a fight, and that makes illusionist gameplay a little too easy.
Well, that some points i found discussed in forum and that i found ingame too and i think it would be nice if they were improved.
If anyone think i missed anything, say it and i will edit the post.
Edit: I'll add a few arguments against changes:
1. There are people who like playing as a Godlike character, nerfs would affect this kind of gameplay.
2. Enchanting has an important role in RP, it is required to some people to customize their characters. (i must confess that I thought about making a beggar character that wears rags and dont carry anything, just relying in spells, XD)
thanks


100 skill + perks is like saying your a master of the ability you just maxed, so why be allowed to go past that peak with gear and pots ( only for the crafting skills )