The aliens have launched a Terror attack on a cargo vessel. My X-COM operatives have fought their way into the middle cabins on the deck of the tanker. Three units are grouped together, preparing to breach another room. Suddenly, one of the three is taken under molecular control but opts not to shoot the other two and instead runs into the unexplored room. Now I face a decision: do I enter the room knowing that I will likely be fired upon by my own unit or wait it out, leaving her inside with unknown terrors?
I decide to wait. As soon as my aquanaut comes to her senses she is blasted repeatedly by a Bio Drone until she drops unconscious. Now I face another problem as the room is quite small and there is nowhere I can safely fire upon the Bio Drone without getting caught in its death explosion. But I have a wounded soldier that needs help ASAP so I burst into action. One unit dashes into the room taking only time to grab the unconscious body of his comrade before rushing back out. While the door is still open the remaining aquanaut pulls a grenade off his belt, primes it and throws it right at the base of the Bio Drone before retreating a short ways. The blast from the grenade blows out the walls, yet still hovering in the smoke is the Bio Drone, now able to see my exposed grenadier. Fortunately his Ion Armor absorbs most of the shots that rain down on him leaving him a little shaken but with no fatal wounds. Suspecting that the alien can't take much more punishment he sets up and fires back. He connects and this time the floating death disc goes down in a fiery explosion even bigger than that of the grenade. My shooter is OK but a poor civilian gets caught in the edge of the blast and is killed.
The fighting is over in this sector but there is still drama left. My unconscious warrior is bleeding out but the nearest medic is several rooms away. The medic and the aquanaut hauling her limp form sprint toward each other. Will they make it in time to save her? Yes! He patches her up and pumps her with stimulants to get her back on her feet. Now weaponless, weak and in need of a few weeks off to recover, she is out of the fight; but she is alive.
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X-COM has the ability to create moments like these that are wholly your own. This episode felt like something out of an action film to me. It's complete with heroics, suspense, mad dashes, aliens, hard decisions, explosions and a nameless citizen as collateral damage. Combine the combat side with the also enjoyable base management and research side and Terror From the Deep is truly an excellent game.
However, taken in context of its predecessor, UFO Defense, it is a weak sequel. It is largely just a reskin with some tweaked stats for equipment and aliens. The biggest additions are new environments to fight in and a bit of alien lore. Ultimately it's more like a standalone expansion than a true sequel.
I would be remiss if I didn't mention a few gripes I had beyond the weak sequel issue. First, the game has a few pretty bad bugs, mostly within the research tree. Fortunately there is a small, free, fan made fix for these bugs called XcomUtil that is popular enough that you shouldn't have trouble finding it. And finally, the last place you invade at the end of the game, T'Leth, is just awful. The 2nd and 3rd portions of this mission are seemingly never ending slogs through linear winding corridors and rooms with relatively sparse alien resistance. My units were constantly out of energy from all the running. To top it off you cannot save your game during the final (3rd) portion which made for a marathon of several hours to finish both the 2nd and 3rd maps in one sitting. It left a lingering bitter aftertaste after completing this otherwise fantastic game.