- i would not only display a tag-cloud on the homepage but also top games.

- why do you need people to log in / "register". wouldn't a captcha also do the job of avoiding spam and make the log-in/providing personal data optional. i think it makes it more likely people would contribute

- categories might could help people to navigate / provide contributers with suggestions how to classify their games. it also enables to "surf" the site.

- i don't dislike the design but i would make the navigation a bit more dominant and combine the two logos, combine the picture of the bottles and the title