Many of us play Halo. Avid players may notice the symbol in my avatar appears quite a bit throughout that series. Before Halo, bungie made a game trilogy called Marathon the logo in my avatar is the Marathon logo, as well as the logo of Durandal (the main AI character ib the games). Marathon ha a lot in common with Halo. You played as a cyberneticallt enhanced super soldier, you were constantly aided by an AI, and many of the weapons have traits that were reused in Halo (like the fusion pistol's charge mode).
In fact, the halo gametype oddball is a direct decendent of the marathon gametype kill the man with the ball (both of which use a skull as the ball).
Marathon is old school. Originally released for mac only, the source code was made public by Bungie and you can get all three games for free legally for Mac or Windows. To get them, google "Aleph 1."
You can also get the second one on Xbox Live.
My favorite part of the video game series is the way they executed the crazy AI concept. It's called "rampancy" and it had some interesting stages. Google rampancy bungiepedia for more info.
If you've never played this game you should because it's free, if you just want to try it without full on downloadih everything you can also get a demo off Xbox live if you have an Xbox 360.