I think the initiative bonus from Leadership is to strong, it can effectively double or triple your initiative depending on how much speed you have. It should be more like 3 and 6 or even 2 and 4, rather than 5 and 10.
To the above poster, if you sneak with no AP left most NPCs can reveal you with an AoE, if you sneak and then move halfway across the map they can't. At least this has been my experience, i use a rogue on most of my playthroughs.
I think sneak is very powerful but if it were nerfed rogues and rangers would become to weak. Besides their charm skills, rogue and ranger skills are quite weak and seem like an afterthought compared to several of the magic schools. Just look at barrage as a prime example, its single target damage per AP is about equal to regular attacks and quite a bit weaker than regular attacks if you're using guerrilla with 5 points in sneak. In general you are better off using guerrilla attacks or special arrows rather than the bow skills. Rogue skills seem to have some of the longest cooldowns in the game, at least their final skill is pretty fun if you have someone with teleport.
In its current state, the only thing you gain from high ranks of scoundrel, expert marksman, or man at arms, are traits. Man at arms seems to benefit from them a bit more though.
I'm aware that fleshing out these skill trees, and balancing the skills, would probably make the game even easier in higher levels. I just think this game needs more than just harder AI, though in some cases it needs that too.