Elite

The Good
What's so special about Elite? Sitting hour after hour, day for day in front of a computer, reading a book, drinking coffee, every now and then throwing a glance at the monitor, to look for potential threats or the space station.
Well it's a little bit paradox, but I think in Elite the repetitive gameplay adds to the immersion.
You start out so inexperienced and poor and struggle to earn your first credits, cargo bay, beam laser, ... . And while struggling you learn how to handle your ship. And with time passing, suddenly you are a flying killer machine, shooting whole armies of pirates, before they even leave their one pixel state. And you feel rather cool doing so :-).
Add in unrestricted freedom to do what you want (be it mining, or piracy, trade or ...) and you have one of the greatest all time classics ever developed.

The Bad
After a long, long time it really get's boring.

The Bottom Line
How to make a living with a space ship or a 3D-space-action-shooter-trading-game placed in a universe of 6000(?) star systems.