Alien Trilogy is based on three popular (Alien, Aliens) and not so popular (Alien 3) movies. The basic idea of the game is to run around the levels hitting switches, collecting items, and killing any aliens you come across. If this sounds anything like Doom then your right, but Alien Trilogy goes a few steps further than Doom. At the start of each mission you are given a set of objectives to complete which vary from level to level. These can range from clearing away barrels, collecting ID tags, etc. The addition of these objectives give the game more than just a "kill badguys, find exit" feeling.
The graphics in the game are above average. Different colored lighting and breaking glass are some of the cool effects featured through the game. Some of the aliens themselves appear a little choppy and pixellated at times, but this isn't a huge problem. The weapons don't look so hot either, they look hand drawn and very fake looking. The sounds in the game are excellent, although the aliens don't scream when they die. All of the guns and weapons sound cool and the in-game music is perfect.
Overall the game controls fairly well and the setup of the buttons is good. I don't think I'd recommend this game to people who are sick of Doom clones, but if you want something more than Doom then this game is a good buy. Conservation of ammo is important most of the time, so if you like to shoot all the time then this game may not be to your liking. There are more than 30 levels in this game so it's lifespan should be long. This is a well thought out game and is worth a rent if not a purchase.