Even if it does not want to admit it, the developers and the trade press, I can only say that there is a full price Civilization 5 modification is for me which is similar to Alpha Centauri and mostly plays so!
Good old Fungus is now miasma; Psycho viruses were replaced by various aliens; epilogues of the planet are now Story Quests; Nessus mine and Co were recycled; transcendence victory is also back on board etc .......
Allen like the Civilization and Alpha Centauri know I strongly advise before buying to test the DEMO (on Steam available)
And think of all the about buying: rather wait until the game is a budget version or just continue playing or Alpha Centauri Civ5!