1. Challenges. They have no place in 40k. This is not fantasy. If you want challenges play tracking fantasy.
2. Hull Points. Worst rule ever! Makes vehicles WAY too vulnerable. Especially walkers. Too slow and not enough armor.
3. Fliers. Ive played every version of 40k and never seen a rule (s) that break a game like fliers and flying monstrous creatures.
As I said ive played 40k since before it was 40k and have owned every army ever made for the game. This is the first edition that might drive me from the game. Its not any fun anymore.