I intentionally run my games long. I like the long struggle for dominance. I think clicking a button, killing a final boss and ending the game is a cheap way to win. I'm not satisfied until I've slaughtered THOUSANDS of aliens. I have to feel like I've won my planet back.
In EU/EW, I have a squad pushing 600 missions and some of them have upwards of 800 kills. I have a mod that steadily increases the number of aliens per mission, some small ships have around 30 aliens! I never saw a point in rushing to endgame in these types of games. I know my original UFO/TFTD games used to run more than a year. Granted, I used to hex edit mod them, so I did a fair few restarts.
I really got into UFO:ET because of this. You had several tiers of weapons and armor to research. More incentive to play longer, basically. Baddies got harder, and there were a lot more of them.
I'm looking forward to long games in OpenXcom. The sheer amount of customizability this project has added males my head spin. I can't wait for my weekend to start so I can tinker with it!