Generally speaking, preview builds of games are not meant to be played for long stretches of time. They're unfinished code, and often don't have all the pieces in place, meaning it can be difficult to even progress, let alone have much fun. Normally, my rule is to not spend more than a few hours, at absolute most, with preview games, especially if it's a game I'm excited to play when it eventually hits retail, since I don't necessarily want to see too much before it's done.

As with all rules, there are exceptions. In my case, apparently those exceptions involve anything with the words "Civilization V" in the title.

Gods & Kings most certainly has those two things, but it's got a lot more than that, too.

Gods & Kings is Firaxis' full-fledged expansion to the hit 2010 strategy game, which hits stores next month. I don't know why Firaxis chose to create an expansion and release it nearly two years after the original hit shelves, and I don't especially care, either. I've been far too busy sinking way too many hours into this thing over the last week to worry about the hows and whys of it all. After 16 hours of playing Gods & Kings, frankly, I'm just glad it exists at all.

Having not really played much Civ V since it ate up most of my winter 2010, it was disturbing to me how easily I fell back down this terribly time-consuming rabbit hole. Firaxis has been sporadically supporting the game via various DLC packs over the last couple of years, but Gods & Kings is the first major functional addition to the game since its release. That new functionality comes in the form of espionage and religion, two things that slide so easily into the old Civ V gameplay, you'll be amazed they weren't there all along.

Religion is by far the biggest change, overall. As with all things in Civ V, religion is simply a tool you, the master of your particular civilization, can use to help expand, evolve, and conquer. You use faith as you would culture or gold. It's a resource you accumulate by building religious structures and a variety of other things as the game goes along.

Initially you'll just found a pantheon, which is a non-specific religion that provides you a single benefit of your choosing, ranging from additional gold via tithing to rapid expansion via "religious settlements" (which are not actually a buildable unit, but rather a rapidity increase to your existing border expansion rate). Over time, as you accumulate more and more faith, eventually a religious prophet unit will appear in your main city. Like the great artists, engineers and the like, you can use this unit in a variety of ways, though the first time, you'll probably want to use him to found your religion.

You can choose from several different religions, from Christianity to Sikhism, though in truth, the religions have nothing to do with the real life ones. Christianity, for instance, doesn't suddenly earn you a Crusade army. The names are just there for familiarity's sake, and you can even rename your religion, if you like.

Religion is no more complicated than any of the other strategic elements in Civ V. It's just way more sacrilegious. In a fun way, of course.

Founding a religion provides multiple new boosts to whatever categories you're looking to focus on. Again, the options run the gamut from resource building to increased conversion rates. Yes, you can use your prophets, when they appear, to help convert other cities and city states to your particular faith. Depending on your friendliness with the cities in question, this can either be viewed as an act of friendship, or an act of war. Bringing religious followers to city states can help keep them under your wing, while doing so to other major civilizations tends to come with more dire consequences.

As is generally the case in recorded history, forcibly converting citizens of another civilization tends to lead to unhappiness from the leader of that civilization. Fortunately, there are other ways to deal with those pesky rival Civs besides religion bombing them.

One such method would be the newly-designed espionage system. You don't get espionage until a good chunk of the way through a given game, but once you do you'll be afforded spies. Spies are not on-the-board units. Instead, they're largely dealt with via a menu on the main game screen. Going to this screen allows you to move spies between cities you've made contact with in order to learn things like which leader is plotting against which other leader, who is building what, and what technologies are being developed elsewhere. If your spy happens upon a tech that you don't have, you can steal it from your rival.

This, of course, does come with a few caveats. Spies can be caught, and when they are, they die. This also damages diplomatic relations with the rival you're spying on, which may or not even matter in the end, but could be a prelude to war. Also, rivals can spy on you as well. You can build police stations and assign spies to your own city to provide counter intelligence, but odds are at least one or two things will slip through your fingers over time.

These two systems add a nice chunk of additional strategy to the already content-rich gameplay systems of Civ V. They don't completely alter the structure of the game, but rather simply provide new road maps to victory using the same types of strategies one would use in the original game.

There's more here, too. Gods & Kings also comes with nine new civilizations (including Sweden, The Netherlands, and The Celts, among others), a gaggle of new units, and some new scenarios to play through. Including one especially strange one. While just about everything in the Civilization series has had its roots in some whimsical version of our world history and reality, the new Empires of the Smokey Skies scenario is pure steampunk fantasy.

Yup, steampunk. Airships, steam-powered tanks, old white guys with mechanical monocles, the whole nine yards. You play the game as you would any other scenario, but every unit is newly built to fit a steampunk aesthetic. Even the tech tree is wholly its own, allowing you to research everything from galvanomagnetism to the more nebulous concept of "The Great Idea" (which is pretty much just a culture boost).

Did Civilization V really need a steampunk mode? Based on the fact that now you can build military grade blimps, yes. Yes it did.

Like other scenarios, this one features its own set of win conditions. Specifically, you have to capture and hold at least three of five different titles. These titles include greatest wealth, highest producing city, number of policies enacted, number of state-of-the-art units built, and the number of great buildings owned. You have to hold those titles for at least five turns, and once you do, you're the King of Steampunk Land.

The whole thing feels like an extremely elaborate mod, but it's also kind of great. It has a whole other feel to it from the rest of the game that I frankly kind of wish could cross over into the main one. I don't know why, but the idea of commanding an army of steam-powered dirigibles as the lord of the Aztecs just sounds awesome to me.

Look, I realize that as great as all this sounds, it's still an expansion to a game that you likely put down in favor of other things long ago. If you didn't, you wouldn't even need this preview, because you've probably already pre-ordered it. For those who did put aside Civ V some time ago, all I can say is that Gods & Kings is as valid a reason to pick the game back up again as you're likely to ever get. The game itself as as fun as ever, and the new additions feel significant enough to justify not just releasing them as piecemeal DLC. I can't say I'm exactly happy about the fact that Gods & Kings has given me the Civ shakes all over again, but considering I've been having a lot of fun playing through it, I guess I can't complain too hard.

I'll remind myself of that the next time I'm sitting bleary-eyed in my boxers at 3am desperately trying to muster enough coherent thought to decide on my next policy upgrade while my girlfriend is screaming at me to come to bed.