Originally designed to serve as a "final defense" security
cannon, the siege tank adopted a two-stage configuration in its final form:
a mobile assault mode and a deployed siege mode that brought
its massive shock cannon to bear. The immense flexibility of
an armored battle tank that could advance and then deploy itself as heavy artillery was a huge success, and the design was widely copied.
The Crucio has been designed for increased survivability with
an enlarged, reinforced turret and hull. The new turret layout also
features an upgraded assault-mode armament package so that the Crucio can
fend for itself more successfully in an open battlefield. Force deployment
costs for the Crucio have increased over the older Arclite, but the increased versatility of the powerful new siege tank more than compensates for the additional
expense.
"Official" details about armament are:
Builds From: Factory
Armament: Twin 90mm Cannons (assault mode)120mm Shock Cannon (siege mode)
Role: Armored Support and Mobile Artillery
What does this mean for other players, like Zerg?
This is powerfull unit doing a lot of splash damage to basic units. Check the video on Starcraft II page. My approach would be to attac it with large number of units like zergling from multiple directions. Zerglings are fast and they do a considerable damage to buildings. The problem would be in narrow passages where couple of crucio tanks could hold off large number of troopers. Another option would be to use a unit with range longer than crucio's like Guardian.Another aspect mentioned here is that this unit is expensive and hopefuly you won't encounter them very early in the game.
For now we don't know much about Zerg units but let's hope we won't have to wait for too long Blizzard starts publishing Zerg unit details.