Well, it's certainly no Thief or The Dark Mod, but its stealth mechanics are on par with any other sneaker out there. If you're a stealth game veteran you'll manage (after realising, that you need cover or elevation instead of shadows). In some places it even beats Thief (I especially like how guards can be a bit unpredictable, so you need more skill than just memorizing their patrol routes. While i know, that lots of stealth game newbies lament this as something bad, i strongly disagree).