I found shadow priests a strange breed. To be efficient the need mana regen, which requires 13 points out of their tree, and to do passable damage they need to avoid any “non-damage” talents. And to have any hope of not pulling aggro, there is 3 more talent points. Every class has some of this, its hopefully intentional.
Its also redundant. To play at all you need to spend them, which means you’re not really choosing your style, you’re making up a toon much like every other Shadow Priest. This does not make you feel very talented.
However one of the most interesting non-damage talent is Silence, which takes 3 talent points to get because its hidden behind the fear ability. Grrrrr, I can’t even see a reason for this in PvP builds, which I suppose is what Silence might be for, but thats forgetting that so many caster mobs in soloing are rendered useless when silenced, so its darn handy.