I think the jury is still out on the usefulness of Corruption versus other players. I certainly seem to run in to a lot of people who are immune to it, but then that might just be the people I'm fighting.
Where I think Corruption is failing however is versus monsters. I've lost count of the number of (monster) goblins or skaven who are immune to disease and paralysis. And you can guarantee that any big bad probably has a magical pattern these days, so in mass PvE battles Corruptors are effectively forced to only concentrate on the smaller monsters.
There is also a tendency, because of the lack of monster numbers, to up-stat most unliving encounters. Making unliving immune to Halt Unliving (as happens quite a lot) and giving them a high Dismiss/Control rank means most times it better for a Corruptor to just avoid the fight. A bit laughable for the supposed necromancers of the field. And shouting for a control wedge is just asking to get targeted by other players at the moment.
Add to that the average Corruptor has no armour, nor an armour spell, nor an immunity spell they can be granted by other Corruptors, and cannot counterspell. It can be quite dangerous when all your cool spells are by weapon blow!
I love having corruption as a list, but I honestly think it is the weakest of the lists out there. The roleplay definitely makes up for this, but I think the issue does need to be looked at. I don't think the list needs to be changed necessarily (and it won't be until rules 4), but I think careful monster statting will go a long way to making Corruptors feel a bit better about themselves. And isn't that what it is all about really? :)
Dantes of Melnibone
Master of the Corruptors Guild
Magister of the Storymancers Guild