Yet another obscure roleplaying game, I've never actually seen more than one copy of the core rules book. Unfortunately, my friend seems to have mislaid his copy - years ago - and I've been searching for the core rules book ever since.
Though I haven't got the core rules book, I still got the character I created for use in the Aliens rpg. I'll probably add him to this section sooner or later. Considering my general laziness, that'll probably be later rather than earlier.
At the time, I really liked the game mechanics of Aliens: the RPG. At the time, I was intimately familiar with RoleMaster - and though I liked (and still do) RoleMaster, I just didn't like the incessant table-shuffling. Aliens presented a single table that all rolls were done on. Obviously, from my AD&D 2nd ed days I liked rolling dice instead of reading out of critical tables what happened. Aliens presented a single die roll extra, to see if the attack penetrated and so on - and the relevant info was already available on the table that you generated the attack result on!
However, the system did have its flaws. Interestingly enough, I didn't encounter any major flaws in character generation or in play. Instead, the game was lacking in explanations on a particular part of the game - the chain of command.
In Aliens, the common campaign revolves around the PCs (and perhaps a few NPCs, just in case) being a platoon of colonial marines doing various missions (not necessarily bug hunts, but they are sure to pop up after a while in the campaign). Thus, the characters are meant to function as part of a military unit, with specialists, military rank, and the whole bazoo. No biggie, right? Wrong!
After having generated our characters, we (five players) ended up with something like three staff sergeants (or whatever), one lieutenant, and one pilot that was lieutenant or something. How does the chain of command work? Who has command at any given time?
Unfortunately, the rules were very sketchy in that regard. Now, years later, I've done my mandatory year in the Army, and I feel proficient enough in chain of command now that I'll be able to set things straight if I ever encounter such a situation again. However, at that time my experience with the ranks used and whatnots was limited at best - and as the RPG clearly wanted that part to be something of a guideline to how the party should operate, it should have been fleshed out more fully. Perhaps even rules for fudging rank should have been included so that characters knew what their various areas of expertise and command were.
Apart from that, the Aliens RPG was a very enjoyable experience. Perhaps I'll even add my character to this section sooner or later.