BC: A total conversion map centered on the middle east, with the map extending from Greece to India. 16 completely new factions, with 1 old faction (the ERE) completely redone with new units. The new units are breathtaking, and I encourage anyone who's curious to browse through the BC link EF provided and check them out. An Area of Recruitment system prevent the Maharaj of India from recruiting elephants in Jerusalem, or the KOJ from recruiting Templars in Ghazni. Unique buildings like the Hagia Sophia have been added to many settlements. Major trade centers, like Antioch, Constantinople, and Merv, are significantly more valuable than other cities, making them a key part of strategy in the game.

The Mongol invasion is actually threatening in BC, especially if you play an eastern faction like the Kwarezhm Shah. Unit balance and AI tweaks make battle much harder than vanilla, but not quite as good as the best Battle AI mods. Garrison scripts, and a few scripted extra armies in the early game add to the challenge. Titles are included for many but not all settlements, and traits and retinues redone but probably not currently up to the level of SS.

I think that cover the mods strengths and weaknesses well, although I'm sure Ramses could do a better job.