Ive just played missions 6 and 7 (both ways) and i have found that the librarian, despite what he is like on paper, really isnt that good. I see him actually as weaker than sergeant lorenzo, and if he gets into trouble it can cost him a lot of psychic points to get out.

His force field power has come in handy a lot, but the psychic blast is expensive for what it does, and is very situational. prescience is ok but would be much more useful if it could be used in the stealers turn as well.

My suggestion would be just to treat the model on the board as a regular marine, and if you can use his powers then its a bonus. I think half the trouble was trying to use him as some kind of super hero, when really he would be better off just going onto overwatch like his squad mates.