The learning curve is a bit steep, mostly because it is still in Beta and the Civlopedia updates are lagging behind the actual updates so trying to look up information about buildings or units can be misleading. I definitely recommend you try it if you have a copy of Civ 4 collecting dust somewhere.
I still haven't fully explored the depth of the game or tried all the different civilizations, means of warfare or paths to victory. So, civ4 players, have you tried these mods? I played D&D back in the 3.0 days and lost interest, but this mod had reinvigorated my interest for playing D&D. Considering the nature of this forum I would expect all Civ players here to be fans of Fall from Heaven as it is essentially a D&D version of Civilization 4 (based on the creator's homebrew campaign setting). I did a search through old threads looking for one about Fall from Heaven, and was surprised to find it only mentioned a few times in passing, despite there being multiple threads about Civ 4.