Too many games use unrealistic, easy-way-out devices to render concealed players invisible. In many cases, they fade into nothing, or become literally no more than a shadow. In some - ArmA 2, looking at you - they would barely stand up to a cursory glance. But of all the games I've seen so far, only one series has really done concealment right. You might be surprised to know that it's the Modern Warfare series - then again, if you play the game, probably not.
Without a doubt, this is as good as it gets. Unlike ArmA 2, your suit matches the grass sprites perfectly. Colour, density, shape - it's all there. You don't fade as you lie there on the ground, as seen in Empires or many RTS titles. Instead, your suit is what renders you invisible. To discover exactly how effective the suit was in a controlled (i.e. not mid-game in a crowded TDM server) environment, and partially to kill some time, Kolby and I took to an empty server on Overgrown, by far one of my favourite maps and easily the best map for concealment. I had long suspected the suit as modelled by Infinity Ward's artists would be effective, but it wasn't until we put it to the test that I realised just how incredibly so it was.
The guidelines were simple: one of us would stare into a corner of the barn, the other would find a position and conceal themselves. To make things fairer and a little faster, the concealed man would give a rough location so the seeker would know which area to concentrate on; if this didn't result in a find, the location would be narrowed down until the former was standing up and talking the seeker onto his position.
The results were astounding. Even when I knew exactly where Kolby was, I could only just make out his outline - if it hadn't been for the outline of his rifle, I would never have seen him. Numerous times I stepped on him, and when my turn came, he walked past me some six times before I rose up into a crouch; he passed me again twice before I stood and talked him to a point only a few feet in front of me, by which time he only noticed me because the muzzle of my rifle was right in his face.
While browsing Youtube out of boredom I happened upon the following video, which demonstrates this rather well - notice how the sniper remains nigh invisible even when he takes a knee, and how hard he is to see while prone, even while moving slowly:
If only as many developers followed the example set by IW, the gaming world would be a much better place - particularly for people like myself.