Alpha Centauri was really cool. It's a shame it looks kind of garbage compared to today's graphics.
BE tries to scratch the itch but whiffs on what made SMAC actually stand out, which wasn't story or mechanics but how both backed each other up so readily. BE's all about gathering the largest percentage bonus to damn near everything and customizing your faction into a jack-of-all-trades because who *willingly* leaves a weak point in their armor, but that just sucks all the feeling out of the leaders. BE's leaders don't feel as complete as SMACs either.
That said, I still play more Civ6 than SMAC. Beyond the eyeburn graphics, SMAC's gameplay is frustratingly simple and a bit grindy. Warfare mostly just amounts to stacking the most attack units you can afford onto a tile with a defensive unit and skittering them along until they die, killing and looting as they go, and the strong bias towards mobility means stuff like infantry gets pretty much obsolete by the midgame. The AI is either too warlike if you or an ally is near Miriam or Santiago, or not warlike enough if you're distant from them. The combination of combat being just unit spam also winds up meaning a whole lot of micromanagment later on, especially once Fungal Blooms start happening all over. It just eventually becomes a bit of a slog.
I dunno, I like SMAC better as a book than a game, honestly.