Starcraft 2 Walkthrough: Wings of Liberty

About my Wings of Liberty Campaign Walkthrough
I've written about a dozen real-time strategy game walkthroughs, and the Starcraft 2: Wings of Liberty Campaign stands out far above any of the RTS games I've played. Key to its success is its non-linear nature. You are able to approach missions in an order you see fit, only facing minimum prerequisites for a mission to be attempted. This is a far cry from the original Starcraft, which was totally linear and no matter how well you did in a previous mission you could not impact your sucess later.
The Starcraft 2 mission progression and intermission system will be copied for a decade. For once, we can see benefits to performing strongly in a given mission and completing all objectives. This is not only in the form of achievements -- the Credits you earn must be spent wisely between missions because resources are finite. Completing secondary mission objectives that give research points add to the fun -- you must choose between two upgrades for every tier (at 5 research point intervals) that you unlock in the Zerg and Protoss Research Trees. This leads to some degree of customization for the campaign experience.
Because of these intricacies, it would be difficult to write a linear walkthrough for the SC2 Campaign. I'd be confining anyone who wanted to read my work to pursuing missions in a set order. Instead, I won't make any assumptions about what you'll choose when writing my walkthroughs, although tips will be given should you possess a certain unit previously unlocked. Everyone will experience Starcraft 2 slightly differently.
Unlocking New Battles: Mission Prerequisites
During the course of my writing, I've discovered various prerequisites to missions. The missions in the Wings of Liberty campaign are not always available back to back. You may start a line of missions but find the next in the chain is unavailable. You'll need to beat a certain number of SC2's missions before others can be unlocked.
Each mission set is linear, in that there is a mission which must be completed before the next can be unlocked. However, you may find that a mission further in such as Breakout or Engine of Destruction will require enough campaign missions be complete before you can take it on, even if you've beaten the previous missions in the chain.
For the most part, all missions can be unlocked by completing your eleventh mission in the SC2:WoL campaign. Here I'll share these notes, so that you'll see when you can perform a certain mission. These may not all be the bare minimum, but it will give you a solid idea.

Mission Prerequisite Tips

After the third mission in the Wings of Liberty Campaign, Raynor will escape Mar Sara and you will find yourself in command of the Hyperion, Raynor's battlecruiser. From here, you will start to have options through the onboard mission star map. Various sections of the ship will become unlocked as you complete more missions. Unlocking a unit in a mission will enable its upgrades at the armory and its associated Mercenaries should they be available for purchasing a contract or upgrading.

• Four Missions Completed: Mercenary Contracts become available at the Hyperion Cantina (War Pigs automatically available), and Gabriel Tosh's Devil's Playground mission is unlocked.
• Five Missions Completed: Research at Laboratory Unlocked
• Six Missions Completed: Missile Turret Upgrade available at Hyperion Armory, Welcome to the Jungle and The Great Train Robbery Missions Unlocked
• Seven Missions Completed: Save Haven/Haven's End Missions Unlocked, along with Cutthroat Mission, SCV Upgrade at Armory
• Ten Missions Completed: Breakout and Engine of Destruction become available
• Eleven Missions Completed: Media Blitz Unlocked (Thor), which leads to a secret mission.

No matter what path you take through the campaign, all missions will be available by completing eleven previous missions. With that information in mind, here are the mission walkthroughs, listed by chain:

SC2 Wings of Liberty Mission Walkthroughs

Mar Sara Missions
These are the first three missions of Starcraft 2: Wings of Liberty. They are very easy and serve largely to get your feet wet before you pursue some real challenges. Not many people should need a walkthrough of these, but they're here for completion. These are the only missions you're required to do in a particular order.
Liberation Day	The Outlaws	Zero Hour

Dr. Ariel Hanson Missions
These missions are all given by Dr. Ariel Hanson. Her first mission, The Evacuation, is available from the moment Raynor boards Hyperion. These missions unlock the Firebat, Helion, and Viking units. The chain is worth pursing for the Viking alone - they will become your strongest anti-air option. This is very helpful throughout the WoL campaign. Choosing between buying Hanson time to save the colonists on Haven vs eradicating the infestation on the planet makes no difference in the long-run. I would choose based on which research points you need at the time (probably Protoss). It does however determine the final role Hanson will play on board Hyperion.
The Evacuation	Outbreak	Safe Haven or Haven's Fall

Dominion Missions
These missions all pit you against the Dominion directly, and you'll unlock some very nice hardware and the WoL Secret Mission, Piercing the Shroud, in the process. You get the Diamondback hovertank through the first of these, and the Thor walker from Media Blitz. You'll also be able to unlock the secret mission in Media Blitz. In the middle two Dominion missions, you'll unlock the Vulture and Wraith fighter. These two are less than impressive in their use in the Campaign. The Wraith is sadly underpowered and Spider Mines require unnecessary micromanagement for the most part. However, the Thor is worth all the effort. They're expensive, but really hard to take down. Diamondbacks are more situational but great at blasting armor. In my opinion, this line offers the most entertaining of all the side-missions in Starcraft 2 Wings of Liberty.
The Great Train Robbery	Cutthroat	Engine of Destruction	Media Blitz	Piercing the Shroud (secret)

Gabriel Tosh Missions
These are all given by Gabriel Tosh, whose nature is unknown to you at the beginning of the campaign. Completing his missions unlocks the rarely used Reaper, but also the versatile Goliath walker. These guys sport autocannons capable of killing small units easily, and can dominate air units with their surface to air missiles. In the final mission, you'll have a choice: helping Tosh and unlocking the Spectre unit, or helping a Dominion agent named Nova and unlocking the Ghost. I liked the Spectre better, as their Mind Blast's five second stun is pretty useful but I find myself enjoying the simplicity of the Ghost's powerful Snipe ability that can do 45 instant damage to a single target. Either of them are powerful long-range snipers and can both cloak and use the call down nuke ability.
The Devil's Playground	Welcome to the Jungle	Breakout or Ghost of a Chance

Protoss Prophecy Crystal Missions
These missions are all memories belonging to Zeratul. They give you the opportunity to play the Protoss for a bit, and are a nice change of pace. These are all available as soon as you've completed the primary campaign mission, The Dig. You won't unlock any units or earn Credits while playing the Protoss missions, but you will earn hefty Research Points. Because these don't rely on how well you've upgraded your units, or what you've done previously, I recommend you pursue these as early as possible. You can take them up through the crystal in the Research Lab.
Whispers of Doom	A Sinister Turn	Echoes of the Future	In Utter Darkness

Wings of Liberty Required Campaign Missions
These are the primary missions of the Starcraft 2 Campaign. For the most part, the rest of the missions can be skipped. However, you'd be costing yourself valuable resources in the form of Credits and Protoss/Zerg Research and unlockable units. The only choice to make here is between Belly of the Beast and Shatter the Sky. You can either collapse the Nydus tunnels preventing the worms from being present in the final battle, or you can destroy the orbital platform at last freeing you from all Zerg air attacks. Either way, the Zerg will beef up their attack to compensate. I provide tips for both versions in my walkthrough of the last battle, 'All In'.
Smash and Grab	The Dig	The Moebius Factor	Supernova
Maw of the Void	The Gates of Hell	Belly of the Beast or Shatter the Sky	All In