mostly lekmod removes a lot of the balancing issues between civs, and makes it so everyone starts on a pretty even playing field, even as the game goes on. you don't get fucked for not having coal, oil, aluminum, or uranium when they appear later in the game. most of the civs have more defined playstyles, and it's actively updated. Alot of the things that you get during the game like social policies, wonders, and units are also further balanced to promote doing different things instead of everyone doing the same social policies and then warring to win.
edit: a big factor is a community though. lekmod and nqmod have a steam group that allows you to add to games with other people relatively easily. these tend to be pretty serious, and that's more or less why this is being made. id much rather play with tf2 peeps than randoms and be a little less strict