Once you're out of the canyons, The Dig gets going. Ancient forces have left a convenient base for you to capture, and a huge laser cannon, which they were presumably using to bore through the massive reinforced doors of a nearby temple, which allegedly holds an artefact.
At this point, the level settles into a nice frantic rhythm, as you reinforce your position, set to work on the temple doors, and hunker down for the ensuing Protoss invasion.
While it sounds like a simple countdown siege scenario, what makes The Dig so brilliant is the choices it gives you. As an early level, the game's still suggesting the best placements for your siege tanks, but it gives you plenty of little unspoken decisions too.
Some of them are RTS staples - like calculating whether to invest in SCVs early on to harvest resources, or whether to protect both flanks with turrets - but some of them are a lot more entertaining, as you decide when to turn the huge laser cannon away from the temple door to use it on the incoming hordes, aware that with every second that ticks by scarier units are getting cooked up behind the scenes.
The laser cannon's interesting in other ways, too, as its sheer overwhelming firepower says a lot about the way Blizzard's separating its single- and multiplayer components.
While this year's C&C4 allowed you to carry all your toys between modes, meaning you could level a tank up in single-player to then blast away at your weaker friend in a skirmish, StarCraft II draws a line around the wackier units you'll be allowed to mess with in the solo campaign.
It's a smart move if it lets you play with insane gadgets like a 20-storey laser cannon, which would simply ruin most multiplayer battles; it's a seasoned genre veteran admitting that you balance multiplayer for fairness, but that single-player should always have a little blast of excess to it.
Speaking of excess, Welcome to the Jungle drops you onto a planet cluttered with revered Protoss temples - holy shrines which, sadly, also turn out to be a great source of handy Terrazine gas. The mission is simple: send out SCVs with Goliath escorts to collect all the resources, before the aliens discover that you're trampling all over their relics and turn up to give you an aggrieved shoeing.
The end result is anything but simple, however, as the Protoss start shutting down the temple gas vents down one by one, forcing you to take crazy risks as your collection teams fan out across the maps.
As the most efficient way of getting gas supplies also turns out to be the most dangerous - send a bunch of heavily-armed squads to the map's farthest corners as soon as you can - it's not long before the level has become an unpredictable rolling firefight. You pinball from one hectic encounter to the next, setting up hasty defensive walls as your SCVs gather fuel, and firing wildly over your shoulder as you beat a retreat.
Compared to the stately pace of The Dig, it hardly feels like it's the same game, and yet it's the same controls, the same rules, and almost always the same units.
It's unlikely the variation will end there. Other treats in store in the single-player campaign include a level where a nearby supernova means there's a wall of flame advancing across the map as you battle it out with the alien scum, and a planet with a swift day-and-night cycle, which just happens to house hordes of photophobic zombies who rush you in the dark but evaporate when the sun is out.
It's a campaign that seems to be made of snarling vignettes, in other words. As such, it's understandable that Blizzard has decided to introduce yet another strand - challenge missions - to do the traditional single-player stuff, like preparing you for the tactics you'll most likely need when you finally go up against human opponents.
That's the real treat, then. While the Protoss and Zerg campaigns will have to wait for now, it still feels like you're getting three StarCraft games in one this time. Blizzard may have made us wait, but it's looking like it's all been worth it. StarCraft II: still terrifying, still very, very tempting.
StarCraft II: Wings of Liberty is due out for PC and Mac on 27th July.