I have all three Omnibus' and I collect each issue and one-shot off the stand as well, I'm a total fanboy when it comes to "Hack/Slash" and pretty much all of Tim Seeley's stuff, it is all great.
I recently (meaning like four days ago) cracked open Hack/Slash Omnibus vol. 2. The next day I ran out and bought vol.1 and 3 and have subsequently finished them all. I fucking LOVE the comic. I am officially in love with Cassie.