Sneaking may be too effective, but I do like the way it's implemented, with the hilarious bushes, and the greyscale/colour dynamic to indicate lines of sight where you risk getting caught if you enter.
In Beyond Divinity, everyone could sneak from the start, but if you had no points into the Sneak skill, the enemy sight radius was really big. With one point into it, it became significantly smaller. You could sneak without training, but you needed to train your Sneak skill for it to be useful.
In another thread, I'm not sure who came up with the original idea, but it was suggested that stealing enough stuff could get you a negative trait. Here's my contribution to that idea:
Maybe there could be some kind of "Shoplifter" trait you get for stealing 50 items, than another "upgraded version" of the trait at 100 Items ("Thief"), and another upgraded version at 250/500 stolen items ("Kleptomaniac"). These traits would have a negative side-effect for your reputation ( and/or initial disposition), although I'm not sure what the positive sides would be. It should make sense, because if you do it enough, even if no one sees you, there are bound to be a lot of times you steal before or after an NPC sees you and suspicious would rise.
It could also affect merchant prices as well.