Ok, so since the argument over the Shade's ability seems to be spiralling down into the usual circles, let's see if we can take this in a new direction. What builds would the Shade's benefit be uniquely useful for?
You can't deny that the core premise of One With Shadow - the ability to hide in situations where you normally can't - is a strong one. The main problem is the action economy, as has been noted, which makes it much, much worse than other racial powers, even when being usable at-will.
Still, there has to be some concepts it opens up which weren't really viable previously.
I suppose it could be theoretically good for leaders - the ability to move amongst the injured without notice can be handy, and leaders do get access to minor actions for healing that can help them contribute even while using this to hide. Similarly, defenders could make use of this - mark an enemy, and then hide, putting foes in a lose-lose scenario.
Pacifist based builds could benefit even more so, though these days most still make attacks, just ones that don't deal damage. I vaguely recalled some Paragon Path designed around giving out standard actions that couldn't be used to make attacks, but haven't been able to actually find it. If something like that existed, those would be of good use here.
The obvious approach, of course, is to focus on a build that gains benefits for being hidden. There are a variety of feats and other options that take advantage of this. Champion of the Vigil makes for a very nice paragon path. A number of others ones seem aimed at a sniper build, which is probably not a great fit - they can usually get hiding anyway, without needing One with Shadow.
Instead, what about a build designed to hide and then move into the midst of enemies? You give up a Standard action, but potentially make up for it by getting a free Opportunity Attack? Or even more, if you can find a way to stay hidden while making OAs. Not sure if any ways exist, but let's see what we can find...
Shadow of the Wild lets you re-hide after attacking while hidden, whether you hit or miss - though you take a penalty on the Stealth check, and need to be outdoors.
At Paragon levels, Heavy Blade Opportunity lets you use a melee At-Will instead of a basic attack for your OA... such as Gloaming Cut, a rogue At-Will which lets you shift and hide after the attack. It requires taking another feat to let you use a heavy blade with rogue powers, but otherwise sounds pretty much perfect, once one hits Paragon.
Now, Rogue seems a bit counterintuitive here, due to the wasted 'bonus Stealth skill' from Shade. On the other hand, the change to Sneak Attack works well with this strategy - you can get Sneak Attack on every Opportunity Attack you make, in fact. One might even go the Hybrid route, where you aren't stuck with taking Stealth automatically, and can pick up some other useful tricks.
Other useful feats include Mark of Sentinel or Opportunity Sidestep, which let us shift while we take OAs, thus making it even harder for the enemy to figure out exactly where we are.
So, at Heroic levels, we are mainly effective in the outdoors, where we can use One With Shadow, sneak into the midst of the enemy, and then take opportunity attacks aplenty as they walk away from us. At Paragon levels, we can do this wherever we want. The Standard action spent on One with Shadow every other round is made up for by the OAs we get.
We probably want to invest in ways to knock enemies prone or slow them, so they can't just reach our allies and get locked in non-provoking combat. Or we can find ways to move enemies around, so we can slide them away from our allies and then force them to provoke again to get back to the fight. We invest in various options that give bonuses for attacking while hidden or with OAs, and damage should be pretty respectable.
In the end, we spend the combat as an invisible dude in the middle of the field who is constantly stabbing the enemy. And that's pretty cool.
You can probably try and pull off versions of this build without the Shade, if you have enough ways to turn invisible or hide... but without nearly the reliability.
