I have no training in marketing/advertising, but here are some basic criticisms I have of many official game sites.
No automatic animation, no Flash menus, please. Sure, that stuff grabs some people, but I bet it annoys just as many. Sound isn't so bad if you bring it in gradually, thereby offering some warning and time for folks to turn down the volume. Animations and Flash tricks can make the page loads considerably slower. Some people check out a game site with only mild interest because there was a link in an article or email, and those people aren't going to wait long for the page to load.
And most importantly, fancy stuff like that often delays the real hook, the real meaning. While there's something to be said for ads that slowly but methodically suck the audience in, it's generally better -- in a world ever fuller of advertising noise -- to start with the punchline.
It's a mistake to make news about the game the intro page. The vast majority of gamers reading your news have already been hooked, regardless of how recently. That's secondary, peripheral information; details. The first thing visitors should see is the game's core concept -- one or a handful of primary selling points. Returning visitors can either bookmark the news page or skip the old info with one click.
If your game is for a mature audience, don't make the first thing visitors see an age verification prompt. In some cases, that might be unavoidable, but in many cases it isn't. Your intro page doesn't have to be part of the main framework; it doesn't have to be one section of many (News, Media, Forums, etc). It can be separate from the comprehensive site. If possible, show what you can that's age-agnostic and make your main pitch on this separate intro page... then let the player pass to the comprehensive site through an age verifier. As I've said, this doesn't make sense for all games, but at least consider it for yours.
When I say to start by showing the game's core concept, I don't mean just a tagline or text alone, obviously. What exactly is optimal depends greatly on your particular game. Some games must be seen in action to believed, in which case embedding a video (just one, and not automatically played) might be a good inclusion. Don't let the structure and design of your site as a whole over-influence the design of the intro page. If you've got a Media section with screenshots and videos, don't let that deter you from including or even repeating a screenshot or video on the intro page.
On the other hand, a game's core concept might be represented well by something other than facts or footage. Destroy All Humans! is an example of a game that could be advertised with a simple graphic along with the title, since the gameplay is fundamentally defined by the silly setting.
Anyway, what do you think? Do you disagree with any of that? Do you have any ideas for making official sites more inviting, more informative, and generally more effective than what we usually see?