At the time it came out, this game signalled the split between Championship Manager creators Sports Interactive and Eidos, and for many, the decision to stick with SI and not the Championship Manager name was the way forward. Having tested both games, I was convinced this was the better option than CM5, and I believe I was proved right. The game picked up where CM4 left off, it doesn't look too much different, and provided me many, many hours of fun over the years.
I couldn't recommend the game highly enough for any football lover - it will seem complex at first but you'll get into it, and there are hundreds of thousands of people online willing to help if you're stuck.
However, it is of course now outdated by several more recent versions, and to be honest, I would fully recommend paying the extra few quid for FM2008, patching it up and playing the most up to date Football Manager around.