Warhammer magic vs new warhammer 40k psychics

Well, I've been doing some looking around, and I've found a lot of mixed feelings about the new 40k psychic stuff. Some people are ecstatic about the change to be more like fantasy, whereas others say the magic is the reason they didn't do fantasy, and instead did 40k in the first place. I fall under the first group. Being a fantasy high elf player, I love magic, and I love winning... Mostly magic though. So when I heard my tyranids were gonna be getting something close to my high elf's magic, I leapt for joy. Seeing as there are quite a few different psykers I can take (some even as troops) I expect to be dealing a good bit of punishment during the psychic phase, or if it's just part of the shooting, the shooting phase. One thing I am unsure about though. Do you get all powers in the discipline, or do you roll for them? Answer me in the comments guys. Remember, everyone here at Warhammer, Life, and Soda loves you!
For Asuryan!
For the Hive Mind!