Reading and listening via podcasts to the reaction to 6th edition the word that keeps coming up is random.
Supposedly random is a very bad word and instantly discredits the game in the eyes of 'competitive' players.
More curiously the 'competitive' players seem to assume that any random event will be a negative. Curious because those of us who play to win (let's face it everyone does) but don't bother with mathhammer beyond knowing that a 4+ is a half chance, have endured the endless lectures on probability which are always framed in the positive - which perhaps explains why 'competitive' players always seem to favour armies that throw the fewest dice,with the highest probability of success (i.e. they are playing the odds at beating chance).
Because here is the thing, not all the random terrain (which appears to cause the 'competitive' players the biggest headache) have a damaging effect, and may well work to your advantage. OK there is a chance that you might trigger a forest that chases you round the board and eats your troops. But equally there is a chance that the roll will give you something beneficial - Jaded Gamercast highlighted a situation in which a Tyranid army triggered a wood that attacked their unit but the attacks were not strong enough to damage their troops, but was lethal to the army they were facing, so they sat in there doing their thing with immunity.
One other thing that is noticeable is that the gamey players are predicting that cavalry is dead (in 40k terms mech) and that infantry will dominate.
8th ed players may well recall that this is exactly what was predicted for 8th ed. And indeed there are people who bought into it and built massive horde deathstars. Indeed the prediction was that MSU was dead. 2 years down the line the predictions have been shown to be pretty much incorrect, unless you are playing without tactics and just charging across the field at each other.
It will be interesting to see how the game develops.