Well, I think Legion is great and it seems to be far more loyal to the comics then what might seem at first glance.
So living in David's head seems to be;:
1. The Yellow Eyed Man
2. The Father in Shadow / The Astronomer
3. The Angry Boy..
He's displayed 3 powers I think I've identified so far.
My guess is that:
The Angry Boy is telekinesis, the Yellow Eyed Man is matter manipulation, and Lenny is telepathy (as it's only a power he's demonstrated in the contemporary narrative, and easily masked by schizophrenia anyway
I wonder if they're going to go the whole hog and have the father be revealed as Xavier. It seems like they could go that way.