TL;DR: I was raised on this game. It will forever be my favorite PC game of all time.
I would hide under my covers, way past my bedtime, as my older brother played through the night. It gave me horrid nightmares as an 8 year old. :)
The following is an excerpt from an email I wrote to my older brother on 8/26/11: (spoilers below)
"Over 15 years ago we began an extermination of an alien threat known as the ‘Terror from the Deep.’ I am proud to inform you that our mission was completed in a “Superhuman”-ly fashion at 0100 hours this morning.
CAPT KDW “Da Bomb” lead a team of advanced X-COM aquanauts through the abyssal depths of T’leth. CDR Leviticus, LCDR Sigourney Weaver, and LT Tommy Lee Jones destroyed the final life-support pillars and personally escorted the alien mastermind to the gates of hell.
It took 11 months to research and build the Leviathan. In the final month of December, 5 to 12 USOs were detected and engaged daily. From January 2040 (X-COM’s formation) the aliens conducted twice-per-month artefact sites, shipping routes, terror sites, and X-COM base assault missions. Though an alien colony was eliminated for every month beyond June, the entire globe was littered with half a dozen known sites.
This wasn't my first attempt. The original X-COM had a glitch that reset the difficulty to Beginner. The true Superhuman difficulty makes TFTD pretty darn difficult. Add on the fantastic modifications from XCOM UTIL, you face a formidable foe. Here are some of my most notable struggles: **Base defense, first month.**
Initial layout is nearly impossible to defend. Aquatoids use Mind Control. Thermal tazers are required to neutralize your own soldiers. Calcinite (deep sea diver) take 20+ rounds of Gauss Rifle.**Terror attack, first month.**
Live Deep One or BUST. Period.**First Lobsterman encounter.**
I am convinced that it is impossible to kill a lobsterman with gauss technology. They take a minimum 2-3 rounds of Sonic Cannon.**First shipping route or artefact site.**
Even the weakest alien soldiers have better than 100% aimed shot. The cyberdisk (bio-drone) and triscene (dinosaur) are by far the biggest challenge in the game. I have never seen either one miss and both can fire 5+ shots in a single reaction or turn. I’m not sure if they can be mind-controlled (I never broke 100+ MC skill) but they both can move across the entire map to destroy your squad. The bio-drone’s death explosion is lethal even with Mag. Ion Armour. The triscene is probably the most rare creature in the game, fortunately. No exaggeration here: the triscene will absorb 20+ rounds of sonic cannon before it dies on Superhuman.**Medium to Very Large USOs.**
Basically requires Sonic Oscillator. Barracudas often get blown to bits or can’t keep up. Without the advanced weaponry, this effectively ends your game within the month they begin appearing.
There were other difficulties; most of them dealing with Molecular Control / Research / Financial. So – what was the ultimate secret of my success?
1. Hand-to-Hand. This was the best tactic and the ultimate key to my success. Half my squad was equipped with Sonic Pistol / Thermal Lance. The thermal lance costs about 8 TU’s, has 100% accuracy, and turns lobsters into meatloaf. The sonic pistol is extremely underestimated and in my opinion the best overall weapon in the game.
2. Research. Weapons, Armor, MC, Submersibles. Proper order is essential. If researched improperly, you cannot complete the game.
3. Manufacture. Technicians can make certain items (Gauss Cannon, Particle Disturbance Sensor) for profit. With a permanent manufacture base, money is never an issue, only sponsorship to avoid losing the game.
4. SWS (Tanks). They die so easily, but they are by far the most effective scouts. Plus replaceable!
5. Aquanauts. I hired over 300 soldiers over the course of the game. Every initial statistic should be over 40, especially reaction, otherwise your soldier is just cannon fodder. MC strength needs to be a minimum of 80. Any soldier vulnerable to mind control was sacked or sent into USOs with primed sonic pulsers.
Instead of having a full squadron armed with cannons, I found diversity is best. There is no reason to leave anyone in the ship, ever. MC specialists (as many as possible!!!) should be equipped with pistols and following your scouts. When in doubt, nothing beats the old elevator trick or blasting away entire ships with the Disruptor Pulse Launcher. I was surprised to find that the traditionally difficult Tentaculant (STINKIN’ BRAIN) were relatively easy to kill. Their only real threat potential is their knack for sneaking around the battleground unnoticed. Once you’re well equipped, or have mind control, the game is simply an endurance challenge, regardless of difficulty."
Soon, OpenXcom will release TFTD support. I'm anxious to jump back into this game and try some of the truly difficult challenges: No Psionics, Ironman, Aggressive/Sneaky AI, the works. Thanks for sharing in my passion. :)