I made the most of mine by assembling it as a Crimson Hunter Exarch.
In all seriousness though, this is because the Hemlock doesn't fit my playstyle. I don't play lockdown tactics, to stop the enemy hitting me back, I shoot the hell out of them to make sure that there's no-one left
TO shoot back...
Using it in an army where EVERYTHING causes Pinning is a nice use though. provided the opponent doesn't do too much damage to your units before the Hemlocks arrive.
If you're looking to get Horrify in, I might suggest ditching the Shadow Weavers for that Spiritseer. They only have small blast, so they're going to pale in comparison to their larger Nightspinner Brethren.
You also appear to have precious little that can take down aircraft. Sure, there's the Dragons and Spiders, but it's very easy for a flyer to get out of a 12" range. (although the Serpent will play it's part here as well)