I personally didn't think there was anything wrong with 5th edition, just bad codexes.
If I had to pick only ONE reason why I don't like 6th edition, it would probably be pre-measuring.
I don't live in the Austin area and dont see me getting much games in between all the tournaments I would want to go, which would leave me less experienced then the rest of the pack.
I wouldn't want to build a Nob Biker army because my friend already runs one with much success.
I also don't want to build an army, paint it terribly, and drive to austin only to be cheated during a friendly game.
All in all, this is my bow out to the 40k universe.
I hope your son gets much, much, much enjoyment out of them because that is all that is important.
Now Tyson, see how many grammatical errors you can find!