I wonder what capacity stealth and room for sneakiness will be in Destiny. Being a sneaky sniper/backstabber is always fun in open world games. Maybe real oufit camos to blend into environments, active camo, all that. Just nothing OP like Skyrim's sneaking. That's fun, but just too OP.
Also, AI should make logical choices when you're sneaking. If you stealth kill one of a group, the rest find the body, they should not go back to a patrol status. They should continually search for you. Stuff like that. Don't limit stealth ability by artificial feeling limits on ability, rather balance it by smart AI.
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Stealth games are built around accomplishing your task despite having the additional task of not being noticed, this is in contrast to most action or FPS games which are usually built around smashing enemies and being a hero. If destiny's best selling point is it's action game-play then making the player detection better causes more fights, however if destiny is more of a do what you want kind of game then having the AI be easy to dupe, or the only one realizing that there is something wrong is an enemy like the fallen captain that corrals the other enemies into being vigilant. I personally think that stealth and destiny can be a part of the same whole, but I do not think that it will be the primary focus. I also feel that having dumber or limited intelligence AI would be better served for stealth play when the player wants to do just that and discovers that they are good at stealth until they run into the fallen captain example above.