(1) This is it--the last level of the game. Thou hast done well, fellow hiveseeker! This lair is quite different from the last 2 in that there are only 2 powerups resting out in the open--a flame thrower canister and a hypo pack. The rest lie within 3 corridors located near each corner of the level except the corner the queen resides in. [NOTE: More powerups appear in these corridors when they are entered a second or even third time; to make them all appear at once (and on HARD you don't want to do any backtracking), enter the corridor partway, exit, and then enter again. Also, you can follow each of the individual corridors to its end and drop down back into the main room, but there are always freshly-materialized 'huggers nearby. It is much safer to backtrack and go out the way you came in.] Also unlike the previous 2 queens' lairs, all eggs are near the walls of this large room. You won't end up missing 1 out in the middle of the open level. For this reason, you should simply hug the walls (especially on HARD--wander around too much and the number of facehuggers assaulting you at one time can reach biblical proportions). Don't worry about missing any 'huggers by doing this; THEY will find YOU! There are plenty of good powerups to be had, and if you are playing on EASY or MEDIUM difficulty settings you can backtrack to keep your ammunition levels high. There are simply too many 'huggers for the HARD player to enjoy this luxury.
(2) Here's the rundown. As soon as the level starts, select the shotgun. You will be dropping down out of the entrance chamber to the level below, right into a nest of eggs. Shoot the nearest eggs immediately and then deal with several approaching 'huggers. Finish off the rest of the eggs here and move left (sticking near the wall as you go). Just short of the upper left corner (as viewed on the map) is the first corridor. Initially within this corridor are 2 shotshells, a shotgun, a smartgun magazine, and a smartgun. Entering a second time causes a med kit and seismic charge to appear. The queen is not too far away, and you should actually kill her first and then return for the smartgun and ammunition. Once the queen works herself free of the ovipositor, you can run into any of the corridors and snipe at her from the high corridor exit (just make sure you continually back up so that you don't drop down). The minus side of this tactic is that the corridors are too narrow to bypass most of the powerups, so you will have no control as to when you grab them. On the other hand, you can simply stand your ground in the main room and hold the queen at bay with either the smartgun or pulse rifle. [BUG! Occasionally the queen will get stuck against a wall or in a corner. Stop firing and she won't be able to come after you!]
(3) With all the goods from the first corridor in tow and the queen (long may she live) dead, stay left to the upper right corner (the queen's corner). You should now switch to the pulse rifle or flame thrower, since you will not encounter any more shotgun ammunition on this level. There are 3 eggs to the left of her ovipositor (as you first approach it) and a larger group to the right. In addition to the other facehuggers scuttling about here, there will be 6 more that emerge from the exit chamber on your left. There is also a hypo pack here.
(4) Leave nothing breathing and keep forward. You will encounter more eggs and 'huggers, as well as the second corridor, in the lower right corner of the level (you pass the flame thrower canister mentioned earlier en route). This corridor holds 2 derm patches and body armor; hit it on the way back if your armor levels are currently high. (AFTER you grab the body armor, 2 med kits will materialize in the corridor when you re-enter a third time. This far into the game, your health is probably so high that you can ignore them.)
(5) The final (lower left) corridor initially houses a flame thrower canister, flame thrower, pulse rifle magazine, and pulse rifle. Re-enter and another pulse rifle magazine and a grenade appear.
(6) Time to head for the exit (don't forget the armor and derm patches if you bypassed them a moment ago). Revived huggers will be everywhere. Move very slowly to activate them in small numbers. The flame thrower canister and hypo pack can help you make your way if you did not grab them earlier.

Medals of honor to all involved! Enter the exit chamber and enjoy the final FMV sequence.