At the end of the last mission, Horner rescued Raynor, his troops and the stolen alien artefact. He did this by showing up piloting the Hyperion – a large battleship and the mobile base of Raynor’s Raiders.

This is more than just a plot point. With the introduction of the Hyperion, it also introduces us to another way Starcraft 2 differs from the original.

In the original, you’d complete one mission and then move onto the next. In Wings of Liberty, the Hyperion acts as a hub of sorts – a place you visit between missions to customise your forces and chat with characters.

Over the next few missions, you unlock all the following areas of the Hyperion, keeping new players from being overwhelmed.

Campaign currencies

In each mission, there are two resources – minerals and vespene gas. And maybe supply is a third currency of sorts. You can spend them on buildings, units and simple upgrades during the mission. Whatever you don’t spend, you lose at the end of the mission. Nothing you buy or build carries forward to the next one.

So far, so typical for real-time strategy.

Starcraft 2 works the same way but also introduces new resources – credits, Zerg research and Protoss research. These new resources persist instead of expiring and you can’t spend them in missions. You can only spend them on the Hyperion between missions.

Spending credits and research unlocks permanent upgrades for your forces. You can never get all of them in the one play through, meaning your version of Raynor’s Raiders will look different from others’ by the end. It encourages replayability as you explore different combinations of upgrades.

Also – and here’s a big one – it gives the designers an easy way to reward players aside from progressing the story. If you’re fast, good at exploring, able to multitask or simply better at warfare, you can unlock more credits and research. These aren’t essential, so struggling players can decide whether it’s worth the risk to complete bonus objectives.

This creates a feedback loop. The better you are, the more of these campaign resources you unlock, so the stronger you become. If you’re struggling, you begin falling behind. This is fair – people who risk more and achieve more should earn more – but it’s not always pretty.

Armory

The armory lets you spend credits in exchange for permanent upgrades to buildings and units. These upgrades give them a bit more functionality without radically changing how they perform. They’re refinements, not overhauls.

Still, these upgrades add up. A few so-called refinements and suddenly you have a formidable force on your hands. Playing without any upgrades is a significant handicap to your combat prowess and economy.

Cantina

Here, you can spend credits to unlock mercenaries. You can hire unlocked mercenaries during missions. They’re stronger versions of ordinary units, they train instantly and you don’t need the infrastructure for that unit. For example, you can hire siege tank mercenaries even without a factory to build siege tanks.

Mercenaries cost more than their base counterparts, though, and you can only hire a small number of them per mission. That and the credits you spend on unlocking them is money you can’t spend on upgrades for your own forces.

It’s a nice addition, giving players a bit more flexibility and firepower.

Laboratory

Acquiring certain Zerg samples and Protoss artefacts adds to your research points. For every five Zerg or five Protoss research points you get, you unlock a pair of upgrades. Out of each pair, you pick one and discard the other.

These upgrades tend to be wackier and less balanced than the Armory upgrades. That is to say, they’re more fun. Some are great, some are hilariously bad, but all of them add a hint of alien flavour to your all-human army.

Bridge

Here, you can choose your next mission. At any given time, you’ll have a choice of one to four places to go next. This allows you to play missions in different orders, unlocking different units and upgrades at different times.

You can’t play the missions in any order. There are simple rules that dictate when a mission becomes available (eg “complete mission X and any two other missions”). But there are a few subplots in Wings of Liberty, allowing you to jump between them and the main story however you want.

It means the level designs have to be smart. You can’t assume that, for example, the players have unlocked the Firebat unless the Firebat is a prerequisite mission to this. This is good – it forces the level designers to design missions around the unit unlocked in that mission. In theory, the unit you just unlocked is the best tool for the job.

In theory.

We’ll continue with the missions next article.