That article doesn't really say that 404 pages should be useful. Their use is to tell the user that the page doesn't exist. As long as it communicates that in a way that users can understand (and returned a HTTP 404) it has done it's job.

There was a fad for a little while around 2000 where people tried to make 404 pages which would "guess" which page you wanted to visit, search it, or make suggestions.

Not only did these projects leave gaping security holes in many sites but they also seem to confuse many users more than if they had just been a roadblock (often resulting in users going around in circles).

Plus, as another comment said, even Google doesn't follow Google's advice.

First, thanks for comments.

Now, it's a perfect 404 page (Status 404 with simple message body, the game is injected by JS, so it's not registered by any crawlers.) For a better understanding, things that might not be clear for any direct-linked visitors:

Most of the site's content is about classic computing in one way or the other. Also a main field of activity is in interactive web content (including a tradition in porting classic arcade games to JS). So it did make sense to offer an interactive error page, which is perfectly in tune with the main theme of the site. (So it's a perfect check for any item on the check list in the link referred to above.) Also it was meant as a humorous comment on interactivity, as you may either watch the interfering error being destructed to ruins (where the invaders would represent the site and the tank the user) or you could get even hands-on by "reaching trough" the error and interacting with the site (by shooting at it for being so dumb and lazy and not providing the right document).

Also, the error page isn't exactly new, in fact it is as of March 2012. (Which is still quite fresh, considering that the design of the main pages is as of 1999. Yes, I'm a bit lazy with this. But at least there's a current error page.)

[Edit] Just for info: An extra set of touch controls is injected, if a touch-enabled device is detected (supporting webkit/blink-style events or the ms-pointer-API as used by IE10). – For the benefit of SmartPhone- and tablet-users.

To those wondering why the top answer says "No, no it doesn't."– the submission was originally titled "The internet needs more 404 pages like this"

Even Google doesn't follow it: http://www.google.com/alsfkj

It depends on your definition of useful

  Did you ever fly a kite in bed?
  Did you ever walk with ten cats on your head?

  Did you ever milk this kind of cow?
  Well, we can do it. We know how.
 
  If you never did, you should.
  These things are fun and fun is good.

These things are fun and fun is good.

It can be both.

But I agree with you that the useful stuff should be first and most prominent.

Keep your Alans on, it's just a 404 page.