@oshizu - Honestly, it's not even the story-line that takes the most time.
At 7 generations in, the game is so glitched/old that I literally can not play over a speed of 2, and sometimes I can't even use that. Every sim-day I play takes almost an hour real time due to being unable to super-speed the game and needing to babysit the current dynasty sim. With a good 40-50ish simdays left, that's a fairly hefty time investment, at least another 15 hours of game time even if I just ignore the game and let it run in the background for a while (which runs the risk of a dynasty sim dying or somehow otherwise breaking the rules by automatic action).
One thing that I've contemplated trying is just bulldozing the lot and trying to play with a smaller, less complex house. Which, actually, may be worth a shot now that I'm really thinking about it. I'll keep an older copy of the game save, just in case something breaks when I bulldoze the lot... but that might fix the game lag and other issues I have. Or at least help.
The other issue with continuing to play is that its been so long I don't remember where I am... I have my score sheet still, so I can look at that, but it's so much slower having to look up where I am instead of just knowing what to do next. In fact, it's been so long since I played that I'm actually having to relearn stuff that I used to know how to do automatically (like the quick process for getting a Sim "very emotional" for an entire work day for example), which makes playing the game less enjoyable as well. I feel like if I was starting a clean game it wouldn't be as bad since I'd relearn it all as I went, but playing the dynasty again is almost like getting shoved into a job that I don't really know how to do and having to learn how to do it while trying to work it.
Last reason: I've beaten 6 out of 8 generations, and the only hard generation was the first one, and some of the second one. About halfway through my second generation of the dynasty, EA updated the Sims pretty heavily. They made all of the aspirations much easier, which made the game itself much easier, and cut the difficulty of the Immortal Dynasty challenge by a good amount. Myself and some others I've talked with think it's possible to do what I called a Double-Time Dynasty, which is basically the Immortal Dynasty, but with all of the requirements doubled. So, the challenge has been more or less a cakewalk since generation 3, I've done more or less the exact same thing for 6 generations, the only expansion to the game that really added new gameplay was Get To Work, and I have another 15-20 hours of exactly more of the same in my future. I'm bored out of my MIND with playing The Sims in general, and this challenge in particular.
TL;DR A bit of a long and drawn out answer there, but I wanted to be clear why I'm stopping... it's not that I don't want to complete, and I really would like to finish the story... but I'm bored of doing the same thing for hours on end, there's really no new content, and my game save is so old its impossible to play at speed 3.