I have to say I quite like the random terrain rules and I like them a lot more in 40k than WFB.
Partially because I'm less inclined to take particularly this edition seriously but it makes a lot more sense in the context of the game. It doesn't make a lot of sense that there should be more than one kind of magical forest on the battlefield or that you couldn't tell a river of blood or that the soldiers wouldn't know about the terrain in WFB. But in 40k in all likelihood both sides are on an alien planet, each dark area, brooding alien fauna or water rippling with xenos creatures represents an unknown threat.
The risk and exploration of the mysterious terrain works a lot better in 40k's sci-do format. I'm much happier dealing with vicious indigenous alien beasties lurking in the forests rather than magical forests that run around.