People hate Spawn. They're seen as a mindless blob that wanders around slowly and gets ignored because of it. People who believe this haven't fought against Spawn recently.
I run them simply. A unit of 5 with Mark of Nurgle for a reasonable 180 points. They then run up the board and eat something. Thanks to their god awful rules in the previous codex they're a highly neglected unit. They used to wander towards something slowly and flop over dead half way there. Now they move 12" and charge 2D6 (re-rolling for fleet) and couldn't care less about terrain in the way if they tried. Thanks to Nurgle they are now T6 and with 3 wounds each are a pain in the backside to take out. Sure they don't have any saves but boltguns are wounding them on 6's. On the charge (and they will get the charge if you know what you're doing) they are getting between 3 and 8 attacks each. That's 15 to 40 attacks for the whole unit at S5 with the potential for poisoned as well.
I admit they can be a bit hit and miss but you're playing chaos marines expect some random stuff to happen. These guys can be annoying for anyone who doesn't know what they do. I've seen Ahriman cast Invisibility on them and they then proceeded to take out Abaddon on their own (that was some lucky rolling though).
Definitely one of my favorite units, I use Vampire Counts Dire Wolves for the models because they look more nurgley (is that even a word?) than the standard ones and you get 10 for £15.50 instead of 2 for £25.