I remember one when I was at University called "Space Empires 3" (I think). It was a simple turn based resource/space colonisation game where you researched technology, built spaceships, met up with aliens. You know, sorta like Civilisation. That first night I was hooked. I built up a huge empire, which was still dwarfed by a friendly alien one, and all the competition were dead or harmless. Then I realised it was 4am, dragged myself to bed and kept waking up because I was trapped in a dream about the game. I was very tired the next day and left the game alone for a bit.
I returned to Space Empires 3 a couple of days later, started a new game... and lost all interest in it within minutes. Never played it again. Weird experience all round, really.