AliensTC is just one of a few Total Conversions available on the Internet. A Total Conversion takes a copy of Doom, and patches completely new sounds, graphics and levels onto it, thus creating a completely new game. Note: You will need a copy of !Alienate to install Aliens TC properly.
AliensTC, as you would imagine, is based upon the Aliens movies. There have been other games like this on other formats, my favourite being Alien Trilogy on the Playstation.
There is a choice of 4 scenarios. These are "Knee-Deep in The Dead" , "Aliens" , "Bonus Level" and "Thy Flesh Consumed". However, it seems that if you run it on top of DIY Doom, you are taken straight to the Aliens Scenario.
"Knee-Deep in the Dead" is the normal 1st scenario from Doom. However in this incarnation, the monsters have been replaced by Aliens, and the graphics have been altered in places, though the level design stays the same.
However there is a bug on the 5th Mission, which means that you cannot get past one of the first areas without cheating.
"Aliens" is a complete set of new levels. They are all based around industrial and 'organic' areas. The organic areas are very dark, and Aliens lurk around every corner. You also find face-huggers coming out of their eggs. The whole experience is boosted by the occasional sound samples taken from the films.
"Bonus Level" is one vast level, which is set over multiple floors and areas.
And finally, "Thy Flesh Consumed" is the original 4th scenario from Doom, which has been made even harder by the inclusion of Alien scenery and monsters.
If you found that the original Doom wasn't hard enough, you will love this conversion. Almost every single monster has been replaced by an Alien, and they are very, very tough. It is no longer the case of 'some monsters are easier to kill than others' as you need to hit an Alien about 20 times with a pistol before it dies.
As featured in the films, the Aliens have acid for blood, and this shows through in the game. If you blast an Alien into oblivion from up close, it will explode in a shower of acid, taking a fair amount of your health with it!
The most impressive thing about AlienTC is the level design. Right from the word go you are thrown into a huge complex layout of corridors, narrow passages, air ducts and lifts. Things are made even harder by the omission of the colour codes on most of the doors that need a key to open them.
Overall: Very scary, and almost impossible in places, however the occasional bugs spoil it.