Ok.. Alien game... Original X-Com (and to a lesser extent, Terror From The Deep).
Different types of aliens, all with different strengths and weaknesses that were explained through the research and autopsies you performed after facing them. And the big bestial ones were tied in as being the support for the more intelligent ones, similar to how police use dogs and horses (to bring it into human context).
The whole idea of "alien culture" not being portrayed well enough... In RPG games, where exploration and interaction with all types of people is to be expected, yes they shouldn't skimp on that. But in terms of action movies/games, where you are facing solely SOLDIERS, different cultures isn't necessary. Soldiers are usually part of an army (as humans understand them), which would imply one organisation is behind all this military activity. Military is often associated with uniforms for a reason.
And the whole clothes thing... It's been said before, we NEED clothes to survive because we don't have the capacity to warm ourselves in cold environments. But put us in the tropics and most people, even if brought up in society based around fashion, clothes and self image will probably strip some of those layers off because our bodies DO produce heat, but coupled with the temprature outside we can overheat. Who is not to say X alien can regulate their core temprature, and have evolved beyond the need of clothes?
And from psychological standpoint, without that taboo you don't feel conscious of your nudity, whereas if they aliens caught some humans with they pants literally down, humans would feel the need to cover up before finding cover.
