Absolutely swap shadowfall for stealth. Not only is it's concealment greater than stealth it also offers resistance to energy/negative energy and psionic damage (one of the few things in the game that does). Slot it for endurance and damage resistance and learn to love it 
Oh and whilst it doesn't stack with stealth it does with Super speed (but only in PvE) making you nearly completely invisable.
I miss him in the weeping of the rain;
I want him at the shrinking of the tide;
The old snows melt from every mountain-side,
And last year's leaves are smoke in every lane;
But last year's bitter loving must remain
~Edna St. Vincent Millay
Great, thanks for that!
Now to find a group doing a respec... Long past time for my first respec at level 30!
WIll quite possibly be doing second respec at weekend again shoot me a tell and will let you know
I picked up Shadow Fall at 18 on my MM and its amazing. Unless you only solo the fact it's an area stealth will come in handy when you're teaming (it has a wide area - as an MM it means my bots are stealthed as well, and gain the resists/defence from it too, which can be very handy).
The resists are very noticeable, even unslotted - iirc the protection to Energy, Neg Energy and Psionic is 20% base and over 30% 3-slotted (that's better than some Brute toggles).
I have a dark/dark corruptor and picked up Stealth some time ago. I'm thinking about replacing it with Shadow Fall during a respec and am wondering whether the only difference is it's a bit more expensive on endurance to cover the AoE? Is Stealth significantly better for soloing? Is it worthwhile to keep both for switching between solo and team play?
Thanks,