Fallout has had some loose involvement with aliens during the series, but the Mothership Zeta expansion is the first to directly involve the player with extra-terrestrials. It's also the final planned chapter for Fallout 3, but will the saga end with a (big) bang? Or will it be sucked into the black hole of mediocrity?
As the name would suggest, Mothership Zeta takes place on an alien cruiser. After being roped in with a false signal the player is taken captive aboard the ship. The expansion chronicles how the player manages to escape and subsequently take over of the ship. Along the way there are a few characters to meet, although much like in Operation: Anchorage, they are used for little more than plot devices. Mothership Zeta actually shares many elements with Operation: Anchorage. It's very combat-heavy, in fact there aren't any plot-related choices the player makes other than to kill "innocent" worker aliens. Even the regular aliens don't speak any sort of intelligible language, so even though they're a clearcut enemy there's no moral grey area as with other expansions.
Where the greater Fallout 3 expansions excelled are in exploration and storytelling, Mothership Zeta misses the mark on both of those with a linear story and section-driven environment. There is almost no opportunity for role-playing as it's focused entirely on objectives. While the combat is enjoyable, there isn't any variety to it and the aliens are very weak, it only takes a few shots to take out even the strongest of them. It's surprising that Bethesda chose to go the same route as Operation: Anchorage, seeing as it was the least popular expansion.
Although it has its shortcomings, Mothership Zeta is still a fun and interesting experience, to say the least. The first encounter with the Abominations, the Death Ray battle, and the final battle are all absolutely fantastic, and are worth it to go through on other characters. The spacewalk, although fairly boring in terms of gameplay, gave such a great view and sense of scale that it merits honourable mention. It's these moments that really help to define Mothership Zeta as a solid expansion, but it's a shame that there are only a few of them.
One of the biggest drawing points of the Fallout franchise has always been the items and armour and as far as Mothership Zeta goes, the collection is fairly average. The Destabilizer is one of the best guns in the game, with an enormous clip size and great damage, but there's nothing really to differentiate it from any other guns in the expansion. There's a very cool set of Samurai Armour as well, however to get any sort of distinct outfits killing allies is necessarily, which might be out of the question for some characters. Even if alien blasters aren't in a player's style, the Alien Epoxy found around the ship can bring any other weapons up to 100%, meaning that aging Gauss Rifle can be restored to its former glory. It's a nice feature and helps to create an endearing quality.
However, there isn't really much reason to play through Mothership Zeta again. As the story is extremely linear, there isn't much scope for diversity. There are a few extra perks to gain, and the Alien Epoxy could help to make further play-throughs more unique, but it doesn't really feel enough.
While Mothership Zeta wouldn't be a first choice for someone looking to purchase their first Fallout 3 expansion, it does provide some interesting set pieces and a few reasons to re-visit the area. It's not particularly difficult, and it certainly doesn't bring anything ground-breaking to the game, though it's still Fallout, and the last scene will blow anyone away. In the end, it's not the best of the Fallout 3 expansions but worth picking up, if only to experience some more of the Fallout 3 lore.