Psi-tlane thas been split in two - the material in the rulebook gives you all the basic rules for psykers that you will generally need, plus provides enough powers and feats to keep psi-talented characters going. Basically, they are a range of telepathic and pre-cog powers derived from the comics.
However, I am currently about 75% through The Rookie's Guide to Psi-Talent - and there is going to be some pant wetting powers in there

If you think back to the comic strips and think about the ultimate in psi-power portrayed, this will be close. Pyrokinetics can set entire blocks or refineries alight, dimensionalists can summon hideous psychic entities, Telepaths can completely overcome the mental defences of their victims and telekinetics can hurl whole mo-pads through the air. Oh, and pre-cogs can peer far into the future.
This is all, of course, high level stuff. At all times, we try to remain faithful to the comics and the low to mid-level psykers will provide many interesting abilities as characters, while not being unbalancing. The comic strips tend to either feature psykers heavily, or keep them more in the background - with the game, you can follow either path as well.