Commander Shadowsun is an interesting option. "Pop two tanks a turn, wow!" you may think, but we'll examine it all in detail. First of all, the stat line. She is basically a shas'O crossed with a stealthsuit. Take a commander profile, subtract 1S 1T and 1W and add 1I. You now have shadowsun stats. Now, what you DO get is two, non twinlinked BS5 fusion blasters that can fire at different targets, two shield drones, a command link drone, a shield generator and a stealth field generator. Sounds like a lot right? So you basically get a heavily upgraded multi-tracker/targetlock combo, a bonding knife, a shield generator, two shield drones, her bonus drone and two fusion blasters. What you trade is 100 points, 1S (who cares?) 1T (TERRIBLE for ID) 1W (who cares? it's S6+ that's gonna take her down). Worth it? Let's look at the pros and cons.
-She can potentially take down two tanks a turn, or can get an almost-guaranteed kill against one (even AV14). I put so much stress on potentially because you're probably only getting into 6" melta range of one per turn, and S8 AP1, even at BS5, can only do so much without the melta rule. It would take an extremely lucky deepstrike to make that happen.
-stealth field generator can keep her alive a turn or two longer than normal. Also means non-assault units attack after her, which could make a difference in very specific circumstances
-Pretty good for sniping Space Marine non-eternal warriors, as two BS5 AP1 ID shots is always nice.
-Her command-link drone is useful as it boosts morale but only when you choose. This means that if you want a unit to flee and get swept in the advance, you can, and that if you want them to hold until your opponent's assault phase then die, you can keep them in the fight too.
-Two shield drones
-Very expensive. Comparable in cost to Lysander or Kantor, who are just so much better than she is.
-Can only deal with TEQ and tanks, no anti-infantry/horde capability whatsoever.
-Can face ID from Plasma, grenade launchers, autocannons, acid spray, brainleech worms, flesh hooks, ripper tentacles, flamestorm etc. that weren't a problem before.
There are two primary ways to employ her:
Firstly, you can deepstrike her (preferably with a PF devilfish with LoS) next to an expensive vehicle and try to get your points back in one turn. Risky, but awesome when your opponent sees this little white armoured mecha-princess drop from the sky and toast his land raider.
Secondly, use her in a support role rather than a combat role. Use her huge 18" LD10 bubble to keep an entire gunline on the table. Would be awesome if it effected kroot.
Is she worth it? Personally, I leave her at home, but she's not so bad that she's unusable per se.