I say stealth is almost perfect in that game although half the time once you get adrenaline powers n shit your runnin and gunnin anyways but still they say those fucking mercs n shit can see you a mile away in a tree or a bush when thats complete bullshit.
Sneaking is perfect in that game and the people who say it isn't are either paid to say it or are just really... really... shitty, at sneaking...
Hell I've sneaked in the bushes practically right in front of them perfectly without them noticing its just about not making any fast movements.