X-Tension is the expansion to X Beyond The Frontier and this is where the series really really begins to take the shape we know from the later games. Multiple starting points have been added as well as the ability to change ship at your leisure making this a much more smooth and enjoyable experience than Beyond The Frontier.
The graphics and interface have received a major overhaul not only making the game far more pleasant to look at but also much easier to figure out.
The addition of multiple starting points now allow you a bit of an advanced start if you have to restart as well as the ability to specialize before the game has even started. This all goes a long way towards making learning the game a much easier experience. Satellite control systems now means you have the ability to manage your interstellar trading empire from a distance without the need to dock with every station you own to check on it's progress and this automation feature also helps makes the gameplay feel much more smooth than it was in Beyond The Frontier.
A heavy duty AI improvement makes every part of the game better and the new addition of random missions gives a little purpose to those players that aren't completely satisfied with the open and unstructured nature of the game.
This however is all just an appetizer when put against the biggest change of all. You are no longer confined to a single ship for the entire game. In X-Tension you are allowed to change ship at a whip and practically every ship you see in the game can flown, from the light scouts to the heavy fighters and the cumbersome traders you can now chose your ship to match your mission and this makes the game much easier to play in a huge way.
All in all X-Tension is the game that introduced many of the concepts we now associate with the X series and in many ways it really is the game that made the series the industry standard it has become today. It's not a game without faults but for it's time it was a huge deal and a great game that holds many fond memories.