As the first part of the three-game series, Wings of Liberty focuses on the Terran race. That means there’s only one campaign, but on the bright side, it is longer and more focused than it could be if it was only 1/3 of the game. Rather than spending a few missions learning and briefly employing a unique set of units and tactics, then being made to switch to a totally different one, every aspect of the Terran play style is gradually fleshed out through a lengthier single-player game. The result is smoother gameplay progression and a fully-realized story arc with a beginning, middle, and [open] ending.
Raynor’s liberated battlecruiser, the Hyperion, is your base of operations throughout most of the campaign. You spend time between missions talking to companions, absorbing backstory through fictional news casts and knick-knacks on the walls, listening to music from the jukebox, or even playing a full-fledged arcade minigame. There are more important things to do on the ship, though, such as patronizing a grizzled mercenary contact in the cantina, buying upgrades for your units in the armory, researching new technologies in the laboratory, and accessing current or past missions via terminals in the bridge.
There are 29 missions in total. Some are not required to complete the story and some are not available during your first playthrough. (At several points throughout the campaign, you will be presented with a choice of two mutually exclusive assignments with different rewards.) You start out with only basic units and tech available, but each mission unlocks a new one for you to use from that point forward. Then, if you choose to go back and replay a mission, you can do so with all of the units you have acquired. Earlier levels may become easier this way, which could be considered a good or bad thing.
Completing missions and/or bonus objectives within them can earn you precious credits, which you spend on the aforementioned upgrades and mercenaries. Unit upgrades can unlock new abilities or fortify attributes and are applied across the entire campaign. Each group of mercenaries represents a supercharged version of certain units, and once you hire them, you can call them in to fight for you during a mission. They are summoned instantly for a premium over the standard unit and also have a cool-down period, but they are affected by the upgrades. Keep in mind that you won’t get enough credits to buy everything, so you’ll have to choose carefully!
No two missions are exactly alike. They’re all made up of unique scenarios that often involve a lot more than simply destroying the enemy. You might be defending your base and holding out for extraction, protecting colonists from Zerg invasion, stealing a Protoss artifact while they are distracted by Zerg, etc. One of my favorites involves a massive Zerg infestation – you go out and raze defiled buildings by day, but once the sun goes down you must retreat to your base and fend off the nocturnal, shambling infected populace. I don’t want to spoil them all, as most are surprisingly fun and interesting.
There is a Protoss mini-campaign (series of four missions) within the context of the story that has you playing as that race. It’s a refreshing diversion, probably included because theirs will be the final game in the trilogy… I suppose Blizzard didn’t want to make us wait too long for some new energy-bladed story action.