Professional style is encouraged. While not as strict as Wikipedia in this regard, the STALKER Wiki is also an encyclopedia and as such needs to represent a certain level of quality.
Use third person when writing about the player. Keep in mind that this is a website adressed also to those, who don't play STALKER and just want to learn about the series.
Use formal English. Articles are supposed to be encyclopedic entries, not forum posts. The occassional sarcastic comment or jab is fine, but don't overdo it.
If you really need to make a joke, make it a smart one. If the article really needs a humorous part, then ensure that it is subtle and tasteful.
Link to articles once per section. To make reading easier, limit the amount of linking to the same articles. For example, if a character's name is mentioned once in the infobox and five times in the article, then link to that character's article once in the infobox and once in the article.
Infoboxes are good. When creating or editing an article that doesn't have one, check the infobox template category and add an applicable one to the article.