This is still under active development, there is a thread going in the main Modpacks forum.
I played ROM, and RI is a lot more polished. Has fewer aspects than ROM or C2C (did not try C2C), but it still greatly expands the main game, better AI than stock, well balanced and expanded science, many new civs and leaders. New promotions, super large world map, religions adjusted and many other points (some stuff removed like Corporations). Really well balanced Civ IV version, to me the best there is, and in principle good enough, Civ IV to its maximum potential.
If this was multithreaded it would be Civ V that I wanted. Anyhow, I play it exclusively for the last year or so, really great, almost like chess - never gets boring.