Bottom Line... I have been playing Civ since 3. Civ4 had mods being developed that were unique and professional. Fall From Heaven 2 was of course THE best mod created. But other mods such as Rise of Mankind and Caveman2Cosmos were so different then the original it was hard to even compare it to the original game. When they released expansions we all wanted to get them right away because it was more assets modders got to mess with. And of course better mods would come out.
A total conversion of Civ5 has NOT been created yet. Alot of mods have changed alot of things to balance the original game and show more info. But none are anywhere near the quality of civ4 mods.
I have to blame Sid for this. Because its his game and it was his choice to release the game with very limited mod support. His choice to make the game engine unforgiving to modders. And if he didn't know its still his fault. You put your name on the box and you are claiming responsibility.
Ultimately it comes down to one thing that proves my point best.
WE COULD ADD ALL CIV5 FEATURES TO CIV4 with the exception of hexes.
This simple fact should prove to you the better engine is still Civ4.
In all of this I have to say its rather sad that I prefer civ4 over civ5. I liked 1upt and the new ranged combat system. On another note I miss Kael and I wish he had been hired by Fireaxis instead of Stardock. Another ball dropped by Sid.
edit: And then there is this
http://forums.civfanatics.com/showthread.php?t=488444