I wish GW would stop doing Chapter codices first and work on:
1. Necrons. Right now, they're very boring, and their tactics consist of move-shoot-move-shoot. The only people who really play them are the ones that like the fluff and looks.
2. Dark Eldar. 2nd Ed. Codex.
3. Better Inquisition. They should just make one Codex: Agents of the Imperium that has Malleus, Hereticus, ORDO XENOS (which should have come out a long time ago) and most importantly, ARBITES. Why? Because they're awesome. Police brutality in the 41st millenium FTW.
4. Codex: Xenos, with minor races like Hrud, Thyrrus, Kroot and such.