Championship Manager 3 is the most ridiculously in-depth computer game ever developed. It allows you to take control of just about any European football team, playing the part of manager/coach.
There is no set goal in the game, just to win as many tournaments and progress as far through the leagues as possible with your team before being sacked. As old players retire, new stars emerge from the ranks of your youth and reserve sides, and a career of 20 years (game time) is not unheard of).
This game develops the themes from Championship Manager and CM2, but it is a game with far more depth than any previous football management game. As well as keeping players and fans happy by producing good performances on the pitch, your progress is followed by the press and watched closely by your board. The detail of this is incredible, a string of poor performances by a star player may cause the press to openly criticise him, you will then be given the opportunity to support or condemn him, with each possible response triggering different effects on fan and player morale. Likewise, the news that the board has given you a vote of confidence should prompt you to look for a sizable cardboard box in which to put your personal belongings.
While you play the game, the AI controlling the other managers in the game will buy and sell players, and makes exactly the same decisions as you do. This AI is one of the best I have seen in a computer game. A more prestigious team will try and poach your young stars from you, and any players who are out of contract are fair game.
In summary, there are few more addictive and involving games for the football fan. This is a dangerous game that you may well lose weeks of your life to. Championship Manager 4 is due out soon (this will be announced by my 3 week departure from life as you people know it :).