First off, I want to say I'm not an expert on 40k. I am not the best player, nor do I know all the tricks and best lists to use. I have been playing since 1998-99 right after 3rd edition came out. I do not remember the "Rogue Trader Days" but I do remember people saying the sky is falling after 3rd came out.
I remember when 3.5 was adapted. It was the trial assault rules and the vehicle fire points. 4th edition came and made them official. It also brought with it the entanglement rules for destroyed vehicles. gunlines were king, and Drop pod armies were pretty good. 5th edition came and brought the rise of cheap transports.
Through it all, my armies adapted, and changed. One thing you can count on during a new edition is the new rules made new troops or vehicles better that were maybe lacking in the last edition. 6th is no different. So after 4 games of 6th, it's time to put some thoughts to paper so to speak.