Normally I have no time for cinematic trailers. Show me the game. This one, though, is oodles of bloody fun. Especially the Dreadnaut flambé scene. And what's that sky-swarm thingy at the end? Could it be? Could it really be... Tyranids? Let there be much rejoicing. (It may just be video blur, but I'm feeling wishful. And 'oh, it's Chaos again' just wouldn't seem to suit that sort of dramatic cliffhanger. Also, see beneath the cut for further, and very strong corroboration that 'They' are indeed our much-desired Big Uglies).
Read on for more 'nid hints...
I'm a little out of touch with Tyranid lore myself, despite having a small 'nid 40K army in the cupboard that I've never used or painted, so I'll hand you over to helpful RPS reader Nick Halme to explain all:
The latest 40k rulebook clearly outlines, in handy-dandy chart form, that the first step of any Tyranid invasion is to release toxic spores into the atmosphere. Essentially, they're acclimatising the planet for themselves, which is not so pretty for the natural inhabitants or...invadees. They then proceed through a number of subsequent steps, most of which involve murderous rampaging, all of which lead to the death of a world.
The end of the Gamespot trailer is a Tyranid reveal, and that swarmy stuff is toxic gas swirling about. The Eldar were no doubt there to try and put a stop to it, or have the Farseer (the chick who got the chainsword to the chest) act as a beacon for something.