I spent a lot of time playing Civ IV mods, particularly the splendid Fall From Heaven, but I've only tried a couple of alterations to Firaxis' most recent entry in the series, and don't think I've downloaded a single one since installing the two excellent expansions to the base game. That all changed this weekend, when a post on PC Gamer drew my attention to the work of modder framedarchitecture, who has created several historical scenarios and a huge Forgotten Realms total conversion. The Faerun mod requires the Gods and Kings DLC and will disable Brave New World when used, and it adds just about everything you could want from a Dungeons and Dragons themed Civ game.
Religions are now Deity Cults, policies are schools of magic and random events include rampaging dragons and other beasties. My favourite part is the selection of Civs though, with 25 representing several groups of the major races.
Faerun is available through the Steam Workshop and is well worth a look. Even with all the enjoyable thematic content though (NECROMANCERS), I did find myself missing Brave New World's features. It's surprising how quickly I've started to think of the new content as part of the game, seamlessly integrated, just as with Enemy Within. Firaxis are dab hands at this DLC lark. Along with Paradox, they're the company most likely to bring me back to a game months after release with paid content, building 'big box' type expansions that add depth rather than length to their games.
There's an optional soundtrack for Faerun, drawn from Baldur's Gate II music.