Civilization Beyond Earth truly deserves the title of spiritual successor of Alpha Centauri. Although it requires a bit of unit diversity, even with the upgrades, you'd still miss the custom unit creation that was available in Alpha Centauri. Factions are diverse but not too distinct from each other, which makes them somewhat easier to get used to quickly. Gameplay and turn times are much smoother than in Civ 5, especially in later phases of the game in a very large map you'd feel the difference of ai completing their turns much quicker.

As i read the comments i see people who haven't played Alpha Centauri but fans of Civ series are a bit confused and calling this an expansion pack of sorts. It simply isn't. Just take it as exploring, or rather migrating to an alien planet because earth is no more habitable and imagine all that 'future tech' in Civ games are new set of techs in here. Sure it takes time to get used to but it doesn't prevent it being so much fun.

It will become a legendary successor when they add more factions, a little more unit diversity and some other dlc add ons but it's still a must buy right off the bat for any Civ or Alpha Centauri fan.

Update as of 23.11.2016 - It's still the closest thing to Alpha Centauri whether you like it or not.