I have recently picked up my copy of the 40k 6th edition rulebook, and so far I am happy with what I see. I think that this edition will cause many positive changes in the community.
one of the first things I noticed was that the game has been reworked in such a manner that mathhammer is gone, not banned from the game, but simply gone. This is due to many factors, including the random terrain effects, allies, and fortifications.
The new terrain rules look to make the game more fun, and will make players leery of 'bunkering down,' as that clump of woods might contain brainleaf fronds which will cause your troops to kill each other.
the allies rules are such that more characterful armies are possible, while limiting the abusive combinations by making it more beneficial to take combinations that are in accordance with the fluff.
The fortifications add a new twist by ensuring that you have needed cover, or better reserves rolls, or anti aircraft fire.
These add up to make the game too complex to boil down to a matter of probability, meaning that you have to play the game, you have to refine your own list, and skill will dominate, instead of "netlists."
The next part that gets me excited is the return of rules allowing grenades to be thrown as shooting attacks, the removal of bracket toughness, overwatch, and other tweaks that will make the game even more fun.
the next few months are going to tell if this impression is correct, with two codices scheduled for release. If they pan out, it will signal a return to 40k being about fun, cool armies, and telling cool stories, instead of merely being a proxy for antisocial tendencies.