Rather than doing it again, it's more like going there again
The second title was disappointingly too sequel-like. It wasn't really too innovative and everything in the game just made me abandon it and start with the first one again.
It was year 1997, when UFO defense got a serious rival. I have to admit, even as I have played the first one a hardcore 100+hours, that Apocalypse knocked me off my feet the first time I played it. It was everything that I imagined the third installment should be, and even more.
The most charming thing about X-COM: Apocalypse is probably the feeling of a totally self-managing community that has everything it needs. The relations between various companies, syndicates and communities change in your playing process and really makes you feel like you're living in a whole different world.