Continuity was not something that bothers them that much when they made the movies.
Well ... yes and no. Between ALIEN and ALIENS, I see no real continuity errors that aren't purely cosmetic (such as the exact design of the Narcissus).
Apart from the obvious, of course: the design of the Alien itself, and the reproductive cycle vs. as shown in the Extended Edition of ALIEN.
The Alien in ALIEN acts alone, and is
much larger than those in ALIENS. The skull carapace is different, as is the configuration of back spines and certain other details.
The Aliens in ALIENS act in the context of a hive, and grow tiny by comparison. They also move substantially differently from "Big Chap".
So ... Cameron thus re-designing the Alien might certainly be seen as a breach of continuity. But it
might also be regarded as an "out" for him to treat them a bit differently — they might
be different.
For all we know, bullets might have been able to rip "Big Chap" to shreds just as easily just as easily as the "Warriors" in ALIENS. We never see anyone try, for good reasons. All we
do se is what bullets do to the "Warriors".
For all we know, "Big Chap" might actually be a "Queen larva" — a proto-stage for a Queen Alien, and thus pretty impervious to bullets
and able to reproduce independently. We are free to speculate — the films don't say one way or another.
There is therefore no reason to assume that the Alien as seen in ALIEN
must react to bullets the same way as the Aliens as seen in ALIENS — there is no necessary contradiction, hence no necessary discontinuity. Thus, they
can be reconciled, without necessarily compromising at all.
Either way, I believe game designers should be in a different situation from filmmakers. In my opinion, it behooves them to
rationalise any apparent discontinuities as well as they are able, rather than use them as an excuse to shrug away continuity themselves.
But, again — such is
my preference. For me, continuity
is important.