All In
This is the final battle of the game and you'll need all of your forces to protect the Protoss artifact. Things will be different depending on if you destroyed the Nydus worms or air units.
Against Nydus Worms
Siege tanks and missile turrets should be your main defense against Kerrigan's Zerg forces. Set these units all around your base, both blocking the entrances, and inside the base itself.
Nydus worms will spawn everywhere, including inside your base. A good amount of siege tanks will take out the nearby worms and their launched ground units. To take out Nydus worms out of your reach, set up startports and make wave of banshees. Send them out and destroy the worms quickly before returning to base. Your SCVs should be ready to repair any damage incurred, as losing a unit is far more detrimental.
Against Mutalisks and Brood Lords
You'll need to concentrate on anti-air. Marines, goliaths and vikings are a strong army to defend your bases. Be sure to also build as many missile turrets as possible. Large groups of these defensive turrets will destroy the waves of mutalisks that will storm your base.
Don't neglect ground forces. Overlords and other Zerg will attempt to charge your base head on. Set up siege tanks to protect any of your buildings. Spare SCVs should be placed in auto repair mode so they fix any turrets or barracks that suffer damage.
As the leviathan hasn't been killed yet, it will storm forward and park itself right in front of the artifact. It will be too far to take down with missile turrets, but they will still prove useful for shooting down the leviathan's projectiles and spawned flyers. Your best option for taking it down is bringing your own legion of vikings and fight it head on.
Kerrigan Attacks
If you become too overrun by Zerg, the artifact can release an energy burst that will destroy them, however it takes several minutes to recharge. Use it sparingly. Several times the Zerg will launch huge waves of overlords carrying ground troops. Your missile turrets should be good for taking out the air units, however if they drop ground units get your tanks or marines on them.
Kerrigan herself will also take to the battlefield. She can install destroy a single unit every few seconds, including tough ones such as the thor or battlecruiser. The best option is to send out an expendable unit, such as a lone marine or build a decoy bunker. While Kerrigan is distracted killing this unit, send in massive waves of battlecruisers and blast her with Yamato cannons. You'll need to continue this routine until the artifact powers up. When it nears 95%, the Zerg will become more rampant and Kerrigan will emerge for a final assault. Continue to hold out and use another blast from the artifact. Once it reaches 100%, you'll have completed the campaign of StarCraft II: Wings of Liberty.
