I think about 75% of what we've heard about 6th is false, namely, close combat AP values (or at least the ones listed), but the most recent set of rumors from grant seem fairly reliable.
I don't like "mysterious terrain:" nobody like dangerous terrain, and the game doesn't need it. When's the last time you played a game and said "Man, I wish I didn't even know if that terrain was dangerous, difficult, or clear!"
Close combat AP values seem like an even worse idea, especially with power weapons being AP3 They make anything with a 2+ save immensely more dangerous in close combat, and power weapons much less useful- there would need to be edits in every codex to increase the points cost of a 2+ save, and vastly decrease the cost of stock-standard power weapons.
If they don't... terminators will become immensely more powerful, as they have both AP2 and a 2+ save, to say nothing of thundershield terminators. Oh, and Grey Knight's ubiquitous daemonhammers will also be a major strength. And Xenos, who have little to no access to either? Nerfed.
I hope none of this is true. I hope GW is smarter than this, and thought this through at all.
Chaos Marines... honestly, legions or not, I'm just glad to see them getting a new codex. And if allies happens, Daemons could get better by being able to pull from their codex!
Anything else that's scratching at your minds? Anything that's bugging you? Let me know in the comments!