Apart from new art and a handful of new combat options, this is exactly the same game as UFO Defense, only much more difficult.
Following in the footsteps of X-COM UFO Defense is no easy task. A modern classic of strategy war gaming, the original X-COM combined an amazing turn-based battle engine with a complex resource management system to become one of the most addictive and innovative games of the last few years.
Relocating the battle from outer space to inner space, X-COM Terror from the Deep creates a scenario where a long-dormant alien race is awakening from the ocean depths. Once again you must take command of the X-COM troops, leading them through battle and managing ever decreasing funds to improve your facilities. Everything that made the first X-COM such a success is still present in Terror from the Deep, but very little has been added to the formula.
Apart from new art and a handful of new combat options, this is exactly the same game as UFO Defense, only much more difficult. The story follows an identical pattern, ensuring that discoveries and important events are easily predicted by X-COM vets. Even though the new alien races and weapon technologies may appear different at first, it gradually becomes apparent that they're the same races and technologies, with new names and new faces.
This rehash leads to some logical errors which are difficult to overcome, especially considering the new aquatic locale. Even though most of the missions take place underwater, you can toss grenades around with ease, and you must develop special suits to allow your soldiers to move vertically (apparently the X-COM training camp doesn't including a swimming class).
Anomalies aside, Terror from the Deep is still a great game, but it seems more like an add-on than a bona-fide sequel. Fans of UFO Defense will find a pleasurable challenge in the cagier alien artificial intelligence, but interested newcomers are likely to find much more pleasure in the original.