I had little trouble mindlessly running through this mission, but it was a dangerous thing. During the run i managed to pick up several pointers which may help you have more units alive for the end. When you start, group all units together and make a second group with just Kerrigan. That way, you can order all units or just Kerrigan. Proceed southwest of your starting location and go through the door. Stay on the southern side of the corridor to avoid the flamethrowers on the northern wall. Move along to the next room, continuing to hug that wall. Use only Kerrigan (cloak her) and take out the ghost on the stairs, proceed through the door to the west and kill the marines, then move your forces on up. Decloak Kerrigan for now.

If you step on the beacon in the northwest side of the big room, you'll see your destination. This isn't that useful now, but it will be later. Now go through the door west of there. Kill the civilians so they don't call for help, then continue through the door in that room. You'll come to some stairs, but should pause before you descend. Cloak Kerrigan and go down them. Destroy the vulture then move Kerrigan down the hallway. You'll see marines on the ledges which will fire at your other troops when they go through the area. They'll be fine, as you're now going to plow the road for them so they can rush through.

At the end of the hallway is a door. There are numerous goliaths there, which Kerrigan can destroy without being detected. Kill them all and your forces can avoid unnecessary fighting. It's a tad tedious, but it's worth it. When all of them are gone, decloak kerrigan then rush your other forces down the hall. Try to stay on the northern side of the wall to avoid as much damage as possible. When your forces meet up with Kerrigan again, go through the door at the end of the room.

In this room you'll find some marines and ghosts firing at you (southeastern side) Use cloaked Kerrigan yet again to avoid any damage to your units. Take everyone up the stairs and rush down the hallway, ignoring the civilian. There are guns that may pop out at you if you kill him. I'm not sure what triggers it (anyone?). When your forces are out of harm's way, go through the door.

You'll enter another big room. In this one are some zerglings you can get to aid you, but you must move quickly. Head southeast along the wall and kill the marines that are shooting at them. Then, go north around the pens to kill the machine guns in the floor. This will allow the zerglings to get out safely. Now go back to the east of their cell and step on the beacon. This will release them. Group all your units into two groups now, so that you can better move them.

Proceed south and round the corner with all your units amassed into one force. Use the attack move command so that they'll attack the large group of marines and missile turrets which will fire at you. When they're all dead you've conquered one of the hardest battles of the map. Now proceed northwest of that location until you see some stairs. Go down them with cloaked Kerrigan all alone. You'll see a locked door at the foot of the stairs. Ignore it for now and kill all the firebats in the big room. You'll want to avoid the room with the doors in which the marines are, as it's a trap.

When all the firebats are dead, move your forces (make sure Kerrigan goes last!) into the trap room. Use the attack move command to kill all the marines and the floor plates, then go behind them and step on the two beacons to unlock doors and activate another security camera. Now go back to the big room and the previously locked door at the foot of the stairs.

The hallway here leads to another part Kerrigan can do alone. Only do this with her alone if she has at least 300 health. Kill the three firebats and the missile launcher. If you have to, use all your units to do it - I preferred to let them heal a bit because they will be practically sacrificing themselves later. Move all your troops into this room now, and head northwest into the beacon to be teleported.

Kill all the marines northwest of the teleporter you exit, but only after all your troops are through. When they're dead, head south down the stairs. Rush everyone to the southeast along the hallway. Kill the marines on the northern side, then pause everyone there to have a look at the area with the supercomputer (it was revealed with that first camera). About five ghosts guard it, but there are also missile turrets in the floor which prevent Kerrigan from cloaking and going right in. Take all remaining units except Kerrigan and rush them at the ghosts. Try to focus the hunter killers on the floor plates. When they're both destroyed, cloaked Kerrigan can go in and finish up the ghosts without being detected. Now it's a simple matter of stepping on the beacon to finish the mission.