According to my source on this one, the rumour about Tyranid strength contributing to the weapon strength was correct. For instance the Fleshborer fires at creature strength +1, while some weapons have no modifier and others have a negative one (still not bad considering many of them are ranged weapons). Some also offer more attacks in combat like the "Scything Talons" my source mentioned, which I assume Lictors and Hormagaunts gets.
Psychic powers wise, all the old favourites apparently make a return from The Horror to Psychic Scream.
Biomorphs and Bioweapons are of course back, apparently there aren't too many new ones though. Bioplasma, flesh hooks, spine fists and all the other nasty living upgrades Tyranids previously got make a return, although now it seems as if more troops can actually get some of them ('stealers with fleshhooks - ouch).