GoldenEye 007

This is without a doubt the toughest level in the game. The time is actually decently lenient, with it taking closer to 7-8 minutes to finish this level without much issue. The real issue is how ridiculously accurate enemies are, and how strong their weapons are. Like with Train on 00 Agent, you need to be fast but careful, clearing rooms and killing enemies without exposing yourself, otherwise enemies will decimate you.

The video below shows the exact route I used, although it has no commentary. Here's a little more of exactly what I did to make this as painless as possible:
 

1. At the start, hug the left side and peek out to the right to shoot the single guard. Doing so will draw over both guards on the left, making it easy to shoot them as they round the corner. Grab their ammo.
2. Open the slab door while staying to the LEFT of it. Peek out to shoot the guy in the corridor. If you shoot 3-4 bullets quickly at him, the two guards on each side will come to the corridor, otherwise they won't. Wait a couple seconds to see if they come, and shoot them from outside the door.
3. Pull out your AR33 and inch ever so slightly to the right while zoomed in, until you can just see the arm of the guard way in the back behind the crates, and shoot his arm immediately, then move a tad more right and finish him off.
4. If you didn't draw the attention of the two guards before, this assuredly will. I recommend switching to your pistol to take them out to save AR33 ammo
5. With three enemies dead from that room, go slowly into the corridor along the left wall. Zoom in at the right pillar, and inch forward ever so slightly until you can just barely see the guard's arm. Shoot it, and move forward a tad to finish him off. Repeat for the guard on the left, using the left pillar as cover. Collect all of their ammo.
6. Switch back to the pistol and open the next door. There are 5 enemies in this room. Fire 3-4 shots quickly into the room, staying back by the door you opened. This should draw 2-3 enemies. Back up to one side and kill them with your pistol. Wait a few seconds to see if this draws the rest of the enemies. If not, go into the room and immediately to either the left or the right, and look toward the end to find an enemy. Kill him, and that'll attract the fifth and final guard to finish off. Collect all of their ammo.
7. Use the console to open the passage. Use your pistol to headshot the single guard in the first hall. Get his ammo. Go down the hall and again headshot each of the three guards with your pistol and get their ammo.
8. At the end, stay out of the room and shoot the left computer console with your pistol 5 times quickly to destroy it. This will draw the two guards in the room, so quickly back up around the corner and use your pistol (or AR33 if out of pistol ammo) to kill them.
9. Head into the room, and the door with shut behind you. Fire a bunch of shots at the left wall of this room to lure guards to you, then head into the vent ahead.
10. Wait at the fork for enemies to come. You should have at least two, but probably three, to kill. With them dead, peak out each side and shoot the two turrets. Head right at the fork to the end to get body armor, then go back the other way to the end, stopping short at the vent
11. This next room is the room of death, but it's not too bad to clear it without taking damage. First, slowly inch forward while zoomed in until you can just see the vent door ahead and slightly right. Shoot the barely visible enemy through it. Then, peek just enough to shoot the turret above that vent. Inch forward until you can just see the turret up above and to the right of the metal crates on your right. You should still be in the vent. Take out the turret close to you, then take out another right behind it in the distance. Now go into the room and immediately right behind the stack of metal crates.
12. From behind the crates, move right a tad and crouch so you can see the guard in the distance behind crates. Take him out. Above him is the fourth and final turret in this room. Peek a bit more to see it and take it out. Now, slowly peek left to spot the arm of the leftmost enemy to kill, then further for the next enemy, and then all the way for the rightmost enemy. Take these slow or they will destroy you. With them dead, the room is clear. Collect all of their ammo and climb up the ladder to close the shuttle doors at the console.
13. Head into the vent opposite the one you entered from. There may be an enemy on the way down, but facing the other way. Use your laser to kill him
14. Now it's time to kill Jaws. Peek into his room to kill one guard, which immediately draws the second that you can quickly gun down too. This also lures Jaws.
15. Depending on your health, you can decide what strategy to use. I didn't run away or kite him. I peeked around a corner while crouched and just gunned him down in the face with an AR33. The AR33 is better than the laser because the automatic fire can stunlock him. Aim for the head/chest to kill him quickly.
16. With Jaws dead, grab his keycard, and now you have to deal with infinitely spawning enemies. Three enemies will spawn and come for you, and when you kill them, the same will happen, over and over. It's therefore in your best interest to speed through the rest of the level as soon as Jaws is dead.

Grab his keycard, equip your laser, and backtrack all the way through the vents, through the corridors, back to the black room. Make sure there are no enemies, then do the objectives behind the glass door. Pull your laser back out and head back to the death room, killing the enemies along the way. Run to the back corner, use the mainframe, pull your laser back out and check one last time for enemies. Climb the latter and pray that enemies don't gun you down from behind. Get around the corner, use the console, and then crouch and pull out your dual lasers and go against the wall, aiming at where you came, while you wait for the timer to count down, ready to shoot any enemies that decide to follow you up.

This is without a doubt the toughest level in the game. Enemies have amazing accuracy and very strong guns. You need to ensure you can get through the first couple rooms with minimal or no damage.