Stopped reading sometime in the beginning of the Icon stuff. Not because I disliked it, but because at that point I had caught up with the issues, and it's one of the series that got pushed to the back of BMB's priority list.
Walker: Jason Patrick (dunno about that choice)
If he plays it kind of like his bit in Narc, that would be perfect, IMO.
Deena Pilgrim: Lucy Punch (have no real idea who she is)
I...would not have guessed this for Deena, but I only ever saw her in Hot Fuzz (and the "play" scene she was in had me in tears, it was so fucking funny)
Retro Girl: Carry Foulkes (who...isn't blonde)
True, but the smile really works, and for Retro Girl, I kind of think that's more important. Who knows if she has any real acting chops, but it's pretty key that we don't really get any characterization of RG until much much later; for 99% of her appearances, it's really only about how the public sees her and what little Walker hints at.
Other parts:
Zora: Alona Tal. Huh, I dunno, I've only seen her in high-school/teen roles, so I guess we'll see. She was good in Veronica Mars, but her being Zora is going to depend a lot on her ability to act much older than she looks.
Johnny Royalle: Vinnie Jones. I would not have thought this at all, but VJ is almost always a pleasure to watch, so I'm good with this.
Calista: Bailee Madison. Don't follow child stars, so I couldn't guess.
Triphammer: Titus Welliver. Perfect. Couldn't have chosen better, IMO.