A couple issues I have with the power armor in DH beta.
First of all, there is only Light Power Armor, there are no options for regular power armor (like in Dark Heresy 1) or Heavy Power Armor (from Rogue Trader: Into the Storm). A little more variety would be nice, please.
Secondly, Light power armor increases the wearer's size, which it did not do previously. I thought that was the entire point of it being light power armor; it's not as protective, but also doesn't bulk up the wearer as much.
Thirdly, the power supply. It only lasts 1d5 hours until it needs to be recharged, which seems inconsistent and silly. It would absolutely suck to go through the effort to get your armor charged up only to roll a 1 on that d5. If it was a consistent 5 hours, I'd be fine with that. Personally, I liked how the heavy power armor (from RT:ITS) did it; it lasted for 12 hours of continuous operation, but required two hours of charging for every hour of operation.
I think the primary weakness of power armor is probably gonna be the Agility cap, even though power armor is supposed to work with the wearer to improve their mobility. I guess those servo-motors and fibre bundles can only do so much, unless you happen to be a Space Marine.