Keep restarting until you start in the place closest to the lasergun (you should be looking at the autorifle right in front of you, but you can't see the laser gun, because it's sitting directly on your right.
As soon as you start here, move right a little bit to pick it up.
Switch to it immediately. If you have 'switch to new weapon', or whatever other one like it, you should bring it out automatically.
If not, manually take it out.
Start strafeing towards the compound, at first going slightly left towards a big pillar thing.
Just before you get to it, turn on secondary fire.
A laser shield will come up. Cool!
As soon as it's on, start moving straight towards the entrance, keeping your shield faced slightly up towards where the lasers are coming from.
You may need to practice a bit, but you shouldn't get hit once.
If you do, restart and try again.

Approach the building from the left, so that if someone was standing in the entrance (which they are!), they can't see you.
Just as you get to it, quickly move to the right and enter the building.
There could be some bots there, if they are, try and ignore them, but if you get hit (which you won't always, because you should still have your shield on) then it's probably best if you restart.
Grab the armour that's sitting to your left, then continue on through the doors which are guarded by laser turrets (which still won't hurt you, thank you lasergun!).
Once your past the doors you can turn of your lasergun for a bit (secondary fire again).
Strafe through the doors on your left, and start making your way down the hallway.
When you get to a part where there's a little opening on your right and left, you can either keep running and get hit once, or quickly turn around, turn on the lasergun, and run backwards while blocking lasers. Your choice.
Either way, continue on afterwards, till you get to a path that leads down and around (you'll know what I mean, it's almost straight after the lasergun).

Start strafeing down and turn on your lasergun's secondary fire again.
While strafeing down the path, try to face the hole in the middle of the room, so as to block the fire.
You'll usually get hit once or twice, but that doesn't really matter.
When you get to end, you'll enter a steel looking room.
Quickly move right, and you shouldn't get hit by the rocket, if you do, restart.
Move left again, and keep moving through into the next corridor. Keep going, but when you get to a small opening on the left, grab the armour in there and keep going.
When you get to the next room (it's small), move to the right, then move to the left again.
The rocket will fire no matter what, but if you do it right, you shouldn't get hit for much damage.

Keep going until you get to a big room.
Move forward for a bit, then move to the right.
Keep going down this corridor till you get to another room.
Move to the right a bit, then to the left, avoiding a big pillar in the middle.
Go through the next part, then take an immediate right up the stairs.
Keep moving UP the stairs, and after two sets of stairs or so, turn on your lasergun.
When you get up the last set of stairs, and laser turret will fire at you, but you should be able to block it with ease.
Immediately Move to the left, and the level should end.

Like I said before, platinum you should easily have.
50 seconds flat is possible, but I doubt any one of you will be getting it, it's very hard ;).
By the way, if you see any guards during this level, try not to get hit.
Whether you go on or not is your choice, just try not to get killed on a good run :).

- Neo