Quick & Dirty guide explaining parts of the game people get stuck on, contains spoilers!
Comprehensive List of Tough Spots
Alright, this is a quick and dirty guide to help people get through the segments that some reviewers either don't understand how to beat or simply struggled with.
First off, aim for the head. Always. It instakills rebels regardless of your weapon or the difficulty. On that note, use the MP7 in bursts or it becomes massively inaccurate.
The part that mentions 'MANUAL ACTIVATION TURRETS' is a -stealth- section. Roll the big spool and quicksave often. You shouldn't have too much trouble following through to the end of it.
In DEAD TENANT, the part regarding the HMG, don't peek it and don't play cute by trying to hide behind props. Sprint room to room in straight beelines to avoid being shot. You will eventually make your way behind it. You can do this section without even being hit by the MG.
Regarding LOW, this is probably the most frustrating part of the mod. Use that prototype AR2 like your life depends on it, because it does. You'll fight your way to a control room which has a lever. Use this to get the wheel you will need to open the grate and move to the next section (You may have to use that lever twice.). Make sure to use the turret in the area to cover your back, because a pair of infinitely respawning fast headcrabs exist.
From there you enter what is probably one of the worst escort missions in history, shoot the living daylights out of the ceiling because there are glitches regarding the barnacle tongues and some of them are invisible, if you keep getting game overs it's because of that. Lastly in all honesty, turn up your brightness. Trying to make do with plain flares and the stalker's headlamp just pure pain.
Once you're through this you enter BAD COP and make judicious use of your shotgun on the vortigaunts you will be fighting. Sprinting right up and double blasting them while they're charging is the most efficient means of killing them aside from energy balls.
Vaccination stations are something that you have to use every so often or Badcop becomes sick. They are infinite uses for healing. Abuse this.
The 'zero gravity' puzzle isn't a puzzle. Use the barrel to block the lasers and take that barrel with you everywhere you go for a while. You'll need it. Once you reach the pod section with the stalkers, break the lights with the E-Balls (this is something I needed help with myself)
From there you should move into the next few boss fights which can be done with just judicious use of bullets.
Tips for the FINAL BOSS, abuse terrain. Jump onto the ammo boxes and onto the HP & Armor dispensers. This is the easiest way to evade the massive AOE attack and the lasers which otherwise need to be ducked under or jumped over. Once you're on the final guy you -cannot- use energy pellets on him or you'll break the fight. Rely on shotgun blasting and just laying into him with your AR2. Try to break sightlines often.
Lastly, the most important piece of advice I can give you is to SAVE OFTEN and mash your quicksave key between fights or whenever there's a calm moment.
Hopefully, if you've been struggling with the game but want to see it through to the end, this will help you.