Sneak is fine. I've had 100 sneak for half the time I've been playing, I can't just wander around under people's noses, it is not overpowered or broken. Even in dark and shadows, and me standing completely still, if someone gets close, they'll see me - period. I mean I can fool draugr pretty well, seems they are always stupid, but, well, they're reanimated corpses, right? They aren't supposed to be smart.
The one thing I can see needing tweaking *might* be how quickly they stop searching for you *if* they see a corpse of a friend. If you shoot from a distance and miss, I can see how they may look for a few seconds and then give up.
but if their buddy sitting next to them at a table just drops dead with a big arrow in his head, and his soul goes screaming over to a dark spot over in a corner 100 feet away (you all have bows with soul svcker enchant, right?

) ... I'd look for a while longer.
also, I'm playing on Master, and occasionally Expert - don't know what the difference is to Sneak in these levels, but haven't noticed that I'm invisible when sneaking with 100 skill at the lowest skill level anyway.