I’m currently playing through the SC2 campaign on Brutal difficulty in order to obtain the Sarah Kerrigan portrait. The first 2 missions were pretty cruisy, until I got to Zero Hour, which caused me to retry a few times.
This mission is basically about holding your base for 15 minutes against an ever growing Zerg army. Now on normal difficulty, you can actually build an army large enough to go outside and kill off all the Zerg forces, but on brutal, this is quite difficult, because at this point of the game, you don’t have Marauders to counter Roaches yet.
Initially the Zerg attack in small waves, until the 5 minute mark, then they get exponetially larger until the timer finishes. Before the 5 minute mark you can opt to rescue 2 (or was it 3?) packs of marines scattered around the map. This is easy.
Build about 3-4 barracks and pump out marines non-stop. Have SCVs on hand to repair bunkers. You can also build supply depots/barracks at the bridge to block off incoming Zerg rushes as well.
Once you hit the 4-5 minute mark, salvage all remaining bunkers outside your ramp. Lift off any barracks and use it to block the ramp. The reason for this is because bunkers have too little HP to tank the incoming banelings. I also lifted my Command Center and used it as part of my wall.
You’ll also need about 2 missile turrets on the right side of the ramp to deal with mutalisks.
At the 1 minute mark, the final Zerg push will begin. At this point your base will most likely get overrun. Just lift up all your barracks and CC as your wall gets destroyed, and make a run for it. Hopefully one of your buildings will survive against the mutalisks and hydralisks attacking it. As long as one of your buildings survive by the end of the timer you will beat the mission.