For the past day or two the promise of a “special announcement” has been floating around on the Interweb regarding 2K and Irrational Games’ underwater epic BioShock. Well, that promise has now been duly fulfilled.

No, sadly publisher 2K didn’t announce that the hotly-tipped FPS/RPG hybrid would arrive free to anyone prepared to legally change their name to Captain Nemo, nor did they reveal that each copy of the BioShock Collector’s Edition would come with its own inflatable Big Daddy and a year’s free supply of Adam.

Unfortunately for BioShock nerds around the globe (GamerSquad included), the big unveiling was much more ‘traditional’ in its delivery and effect. Indeed, while expectant gamers chattered enthusiastically online about the official BioShock Launch Trailer that premiered on Spike TV yesterday (Sunday Aug 12), it was the revelation that a playable demo was also being released to Xbox Live Marketplace that really caught the news.

Arriving as a blessedly free playable offering, Xbox Live subscribers can grab the 1.35GB BioShock download from the Marketplace right now… yes, NOW…though a certain degree of traffic crawl should be expected so don’t anticipate quick processing. GamerSquad would suggest attempting a 15,000-piece jigsaw of the Eiffel Tower (at night) in order to help while away the hours before the mysteries of Rapture are finally opened to you.

Meanwhile, as BioShock’s official August 24 release date looms ever closer, more review feedback is starting to arrive – and none of it is in any way negative.

Alongside existing reviews of note, which include PCZone’s 96% score, and the UK Official Xbox Magazine’s straight 100%, the gurus over at Gamer.tv have now seen fit to bestow another 100% (5/5) score on BioShock. While trumpeting that the game boasts a “hugely atmospheric feel” where the “opportunities for [gameplay] variation are massive,” Gamer.tv ultimately proclaims that Irrational Games’ watery creation has duly “managed to instantly stake its claim as one of the best FPS titles in gaming history.”

Footage provided by GameTrailers.com.