They are quite good for certain builds, but I do hate the flavor. If they'd had weird, shifting shadows following them around (because of their Plane of Shadow ties), instead of stupid glowing runes on their heads, I'd have liked them. But that would be an entirely different racial write-up fluff-wise. Basically, I wish they had the fluff for something like the FR Shade template, which sucks mechanically (due to the high LA), but is awesome flavor-wise.
For a shadowcraft mage, the Improved Sigil (Krau) feat is amazing. It's a free +1 heighten, which is like a free +1 higher level to all of your spellslots for a SCM.
Using transparency, the Krau sigil is also very nice for ardents, as the max power they can know is determined solely by their manifester level. So it lets you multiclass for free for one level without having to take Practiced Manifester. Or you can make up for up to 5 lost progression levels if you take that feat and play an illumian.
The free Divine Metamagic-like ability (twice per day) with the Naen Hoon sigil combination is also great.