The seeds of addiction are still inside me: Once I start to play a decent game, it is no problem to continue playing for ten hours. Such a long session has the effect, that the following day your thoughts keep returning to the game: The cities, the buildings they have or should build, the spells to be researched and cast, the military units and their use against the enemies.
Next I'll tell you some background information about Civilization. The aim of the game is to colonize the world. In the beginning, the player chooses a civilization (say, the Greek) and starts with one city (say, Athens). Then the player expands his civilization by using peaceful and military means.
Peaceful means include building new cities. This kind of expansion is the first priority, and usually the civilizations try to grab as much land as they can. When most of the continent has been colonized, the peaceful options are to develop larger cities and to develop more powerful technology.
Warfare is almost inevitable at some point. The level of technology determines, how efficient weapons one can build. The number of military units depends on the production capability of the civilization - the number and size of the cities.
There are two ways to win: To conquer all other civilizations, or to develop technology very far and to send a spaceship to Alpha Centauri. (The technology development starts with the invention of wheel around 10000 BC.)
It was one of the few games which me and my brother bought legally, so we also had a manual. It wasn't very useful for the gameplay, but it contained a 20-page summary about the history of the human race. The summary concentrated on technologies, as the civilizations rose and fell. It ended with a list of references. The authors had digested a lot of background material. And it showed. Historical aspects were embedded in all aspect of the game, starting from the main structure of the game and the naming of technologies and military units. Naturally, the gameplay itself followed its own rules, and not the rules of the history - the playability is always priority one, as it must be.
These kinds of games can really take a lot of time. There isn't any natural point to stop, and always something interesting to happen in a short time, which makes single playing sessions long. The sheer amount of time used, combined with the complexity of the game, makes your thoughts come back to the game the following day.
In the comprehensive and high school, I could start playing as soon as I returned from the school, and continue the whole evening, but sleeping times set by parents meant that eventually I had to stop. For a university student, this kind of addiction is more dangerous, since no one is keeping you on check. If you skip a lesson, no one cares. If you stop going to a course, the reaction is nonexistent or very weak. Luckily, I stopped playing in the high scool (when I moved to another city), and haven't started regular playing again.
The immediate bad effects of reckless playing are: Loss of interest to other things, irregular sleeping rhythm (since you just keep playing and playing in the evening), skipping all activities where absence is not punished, delaying of tackling problems.
The long-term effects are more speculative. Some people have normal social skills, even if they played a lot as young. If you don't do sports, the reckless amount of time spent in front of the computer makes you physically weak - and the games make you forget that it matters. After certain point, playing doesn't develop any skill, which matters outside the game. If you've just spent 100 hours in the past month playing Civilization, it won't give you any andvantage whatsoever outside the gameworld. If you watch 100 hours of TV in a month, then at least you can talk with other people about TV programs. To sum it up, that it's not the playing which damages, it's the other things left undone while playing.
Nowadays, I play maybe 2-4 times a years. Such a period usually lasts for a week or less. It gives me a reminder, that it's not the way I want to spend my life. After not playing for a week or so, I lose interest, so it's not an urge I have to resist. But when I play I'm like the alcoholic, who can't drink moderate amounts.
I'll finish with some quotes from persons who didn't stop in high school:
Ahh, I failed most of my first year exams at uni because of dune II.
Now I can relive this by being late to work everyday by going to bed at 4 am. hurrah!
Wow. This is like a trip down the memory lane called college. Had I spent half the time on school - nay, a quarter - I would have been a PhD years ago.