I've noticed there doesn't appear to be much discussion about mods here....perhaps that's left for civfanatics? Still I can get here from work and not to cf so here i post about my current favorite mod and I believe the most ambitious mod.
It's created by a team of modders but the original concept was by strategyonly i believe and I think it has links with the Rise of Mankind mod but is now so far beyond RoM that it's silly!
C2C follows the ideal that more is definately better and at version 22.1 is currently sits at about 417 techs, 500 units (I think) and over 1200 buildings and it incorporates many of the more useful UI and performance mods in effort to keep the game running smoothly.
So far I have played almost every version that's been released and I constantly see clear improvements and additions, generally i like the idea of more is better and being a builder/researcher type player this mod has kept single-player civ4 alive for me more than any other game I think I've ever played!!
However there are some little tweaks I'm not so sure about....for the most part the mod has tried to keep with a certain level of realism....certainly up until the genetic and future era....which to be honest has happened yet for us so I allow for a some flight of fancies!
But in the last couple of releases they are introducing "punk" techs, basically alternative technology paths that lead to unique units and buildings that have never existed for anyone but in imagination (I think)....on the other hand far from being any more game-breaking than any of the other additions.
I enjoy the Pre-historic era in which the game is made challenging by the lack of expansion (cannot build settlers and workers can only build 1 thing, then they are removed from the game) and also by the large quantity of animal units which can make map exploration particuarly tricky, it's only later in the pre-historic tech-tree that you get to build a "tribe" which is a limited settler, you can only have 1 at a time, in addition to this expansion is limited by penalties being applied to the number of cities you have depending upon which government civic you are using.
What also makes the game interesting is that culture is a 2-fold process partially governed by your initial choice of civ (American, European, ocenian ETC) and then later defined by techs and nearby resources which will then in turn give you your UBs and UUs....amongst other things, which can make games even more unique as you cannot guarantee what resources you will have near you and thus which culture you would take on.
Later they have a Galactic era planned with promises to be as game changing as the pre-historic era, but I believe it is being held back by what is inherintly possible with the civ4 engine, some of their ideas may not even be possible and thus get dumped, however the team being this wonderful mod seem commited to makign the mod as stable as possible and will do their best to nail down the cause of any CTD not caused by the MAF
If you like mods and haven't tried this one, I highly recommend it....and if you have tried it, please comment and add to what I've missed....the mod is so big that I've missed an awful lot of this first post!