On paper, Gods & Kings looked like a big step forward for Civilization V. I'd watched Civ 5 gain respectability over its first year and a half... there were so many problems at launch, but so many improvements over 18 months, at least for the single-player game. (Multiplayer remains awkward, to this day.)
Gods & Kings looked like an expansion pack that would add some much-needed variety to the gameplay. It delivered a mixed bag of improvements and disappointments.
What I like:
I find that the new City-State mechanics are an improvement. I like the quests, and I like having the new types of city-states. I generally enjoy manipulating the city-states, and vying for their allegiance.
I also find combat to be improved. The switch to a 100-hit point system makes it easier to manage your units in combat. Also, they have reworked naval combat, with clear distrinctiosn between ranged and melee naval combat. This is a big improvement.
What I dislike:
The Religion system starts as a powerful game modifier but quickly becomes an afterthought as time wears on. The system for spreading religion is difficult to understand and control. And when you're playing on a random world, it's hard to predict which benefit is best for your fledgling religion. Choosing the wrong one makes Religion a useless money pit for your Civ. I also find that pursuing a profoundly religious civilization has very detrimental effects on your development -- it takes a lot of effort to build those buildings, and the payoff decreases as the game advances. It's sort of like Culture, except that you can commit to developing Culture and win a Cultural victory. You can't win a religious victory in this game, because it doesn't exist. Duh!
The espionage game in Gods & Kings is terrible. It has no manifestation on the game board at all. You're randomly granted imaginary spies. You choose where they "go" and what they "do" from a huge table of world cities. Occasionally, you get a pop-up notice that you've stolen a technology, or thwarted a coup attempt. That's it. It's about as much fun as manipulating an Excel spreadsheet, because that, in essence, is what you're doing. Horrible, horrible gameplay.
What I don't care about:
More Techs. More Buildings. More Civs. Who needs 'em? Please. Take these back and go work on fixing multiplayer!
A year after the release of Gods & Kings, I find that I play more often with this DLC turned off. The new combat system was patched in to the base game at the same time Gods & Kings was released, which means that the only thing I miss are the better City States. But Civilization V is still a better game without Gods & Kings.