I play the thief in ES, I find that it's the best way to experience the world as you move through it slowly, examining every square inch as you go. It takes time and patience to pilfer anything of use but it's always satisfying when you succeed. The whole point of this class is to have freedom of movement through otherwise inhospitable and secure areas. If you make the world too accessible to other classes, what is the point of playing the thief, other than to roleplay an impotent hero?
Oblivion [censored] in the face of the thief. You couldn't sell anything you stole without having affiliation with the thieves guild and there was a daedric artefact, which anyone could obtain, used to open just about any lock, a giant 'f' you for those who'd spent the time working up the skill and collecting lock picks.
Lock picking should be THE skill for opening doors. Magic is convenient up to a level but it should not expect to be opening lvl 100 mechanisms, let's keep it this way. The grace of the mage is in its utility, not in its ability to do everything better than dedicated skillsets (invisibility is too powerful).
I don't like the idea of dragons being in an ES game but that's fine. The problem is that they're at the top of the hierarchy insofar as enemies are concerned. I hope they aren't easy to kill, I don't care how cool the fight is if a level 5 character can down them, which brings me to my next point. If you make everything easy to defeat, what is the point of playing the thief?
The thief sneaks because he/she needs to avoid confrontation, not because it WANTS to. Some guards should be more powerful than the lowest level dragons, it's about gameplay not 'realism'.
If people can do anything they want whenever they want and succeed, then the game will have failed because it offers no challenge. I understand the need to cater to all these Fable lovers but don't compromise the game any more than you have.