I do not plan to attempt this on Brutal, but here is how I got "Aces High" on Hard difficulty:
Planetary Fortresses: 2 on the right, 3 on the left (plus one supply depot). It's a perfect invincible wall-off. We use PFs for a number of reasons (high health, high armor, mounted cannon), but the primary reason is that they have a very large surface area, so a lot of SCVs can repair one PF at once. The zerg will not be able to break through as long as three things are true:
1. You have enough workers repairing the wall.
2. You have enough minerals/gas to do the repairing.
3. You don't let Kerrigan punch a hole in the wall when she comes.
So once you have the wall-in, here is everything else you need to do to ensure that it remains standing:
-Get full saturation on the minerals and gas ASAP. If you don't, you'll run out of minerals for repairing the wall.
-Put massed siege tanks behind the wall. This will ensure that most zerg units won't even get a chance to attack it. But leave an aisle for the workers!
-Put at least three or four psi disrupters behind each wall. This will also severely limit zerg attacks.
-Note that the two fortresses on the right will be taking way more individual damage than the ones on the left, so have higher concentration there - both in units and your attention. Usually when someone's wall breaks down it's on the right. I barely even looked at the left wall the whole time.
-Place a few missile turrets, plus your starting BCs, back by the mineral line in anticipation of the Overlord attack.
-Create a group of banshees to destroy the Nydus worms (at least two Starports). As long as they are cloaked, they will be invincible for a while (the enemy doesn't bring spores until much later). But even after the enemy gets detection, you can still snipe the spores and keep going. If you do not destroy the Nydus worms, you will still be able to repair the wall and everything, but you take the risk of running out of gas from sheer repairing. I did one playthrough where I did not use banshees at all and I made it to about the 75% mark before my SCVs ran out of gas for repairing the wall (I may have skimped on the disruptors, though, so that could have contributed as well). The next time I played I used Banshees up until 70% (so no attacks reached my wall at all until then, literally - they either got blasted away by siege tanks or never got out of the worm), then it got too hot for them so I just retreated, exposed my walls to full attack, and relied on my stockpiled resources for the remainder of the game.
-Once you retreat the banshees, put them above the artifact to guard it, as nydus worms will be spawning right next to the artifact.
-Use massed marines (built from at least 2 barracks that are on the hill next to the artifact) to distract Kerrigan while the tanks take her out.
-If you get a breach during one of Kerrigan's earlier attacks, no big deal - if you're on top of the nydus worm thing, there won't be any zerg around to run into the breach and you can just rebuild the missing PF. But if it's during one of the later waves, you'll have a really tough time patching it up, so be very careful.
-At the end, Kerrigan will conduct one last huge attack that often trips up players who were doing fine up to then. So what you need to do is: 1. Take all of your workers off the mineral line and put them on the wall. 2. Dump the rest of your resources into mercs and have all of the mercs suicide-rush Kerrigan. 3. Make sure you have some air units protecting the artifact. The mercs will most likely keep her busy until the artifact goes off and you win.
When I used this strategy, my wall was still perfectly intact at the very end and I could have gone on longer. I used my artifact blast around the 85% mark (Kerrigan's second-to-last attack) to reset the map.
Edited by Torloch on 5/24/2013 2:59 PM PDT