This guide covers the most common questions and hints by level. Only read as far as you need to avoid spoilers.
Level 1
Not much to do here. One tricky part is getting security down to 0%. There are hidden rooms behind flat fluorescent light panels which harbor security cameras. For example, go to the first door which required a security code — it's near the surgery machine at the start of the game. There is a flat, light blue fluorescent panel on the floor; step on it and it will lower. There are several of these on this level. Finding each one enables you to open some hidden doors near where the resistance put up its last stand. You can get a Magnum 2100 there, which is a nice piece of equipment.
Tip: Leave on-line help on — it will point out hidden doors as you come across them. They are very easy to miss on the automap.
Level 2
There is a room with a red force door which has some mutants behind it — you can't get in there until several events happen later in the game. Nothing essential in there anyway.
Be sure to use both cyberterminals: one in the library and the other in a room near the red force door. Everything else on this level is straightforward.
Level 0
If you've read your logs you will know about the plan to destroy the laser. The laser and shield controls are on this level — one of the log messages includes a section of map showing the locations. You'll need the isotope from Level 2 to enable the shield. Then you'll need to get to the override switch to fire the laser while the shield is on. Explore Levels 4 and 5 first if you want to amass more armory before tackling these rooms.
Level 3
This is a nasty level — the invisible mutants are dangerous. There are two easily accessible power stations on this level, so make use of your light and shields. Getting the restoration chamber switched back to healing is a priority. There are three elevators on this level: the one you came up on, one that goes up to Levels 4 and 5, and one that goes to Level 5 only. The one that goes to Level 5 probably won't be working initially (power is being diverted to charge the laser). Take the elevator to Levels 4 and 5 — exploring those will give you good weapons.
There are several maintenance doors you cannot open until certain events happen. The headlamp can be found on this level. You'll return here later to do a lot of things.
Level 4
This is the storage level. Lots of good things to be found here. The one tricky part is getting to the plastique. There is a button on the floor (where the tiger gorilla beast was) that activates sections of the catwalks above that you need. Be sure to get the environment suit from this level as well.
Level 5
Nothing particularly tricky on this level.
Level 6
You need to jettison the infected grove. Nothing difficult here. In Beta Grove, if you stick to the right you'll get to where you want to be fairly quickly.
Level 7
Your goal here is to blow up the antennae. The plastique is in the catwalk area of Level 4 (the storage level). You'll need 4 pieces. To use it, double-click on the door on the antenna, then use the plastique and double-click on the panel on the antenna to install it. Once installed, get away from that antenna immediately — the explosion will hurt you if you're standing nearby.
After this, try to proceed to Level 8. You'll find you probably can't get very far yet.
Level 8
To get the locked door open you need to set the reactor to blow up. You'll need the system authorization code to do this.
On Levels 1 through 6, the computer nodes you destroyed were each fixing one digit of the six-digit system authorization code. The digit fixed on each level is shown on a black screen in the room where the computer(s) were. Collect all six digits (from Levels 1 through 6) to assemble the full code.
The reactor is on Level 0. Make sure you have a good environment suit (found on Level 7) and detox patches. Type in the first 3 digits of the code, then the next 3. Then run as fast as you can to the escape pod on Level 5!
