There's a game-breaking bug where if you capture more than 69 cities, it crashes to desktop, and I discovered it the hard way.
I played as Rome on a normal sized map and at normal speed, I was on a continent with India, England and the Iroquois, while on the other side of the world there was Arabia, Persia, France and the Aztec. India declared war on the Iroquois, so I attacked India to prevent them getting too powerful. I only intended to take two cities and make peace, but I wiped out their counter-attack and decided to take their whole empire, including what they "stole" from the Iroquois, and their city-state ally, Vienna. Then, England declared war on the Iroquois, but by the time I had my army on their border, the Iroquois surrendered all cities bar their capital to England. This meant I had to fight England on two fronts, but my army was big enough to handle it and I took them down. Then, like the bastard that I am, I took control of the last remaining Iroquois city.
While all of this was happening, France had become the major power on the other side of the world, but it attacked one city-state too many, and an alliance of city states declared war on France. This hurt the French empire a lot, and Persia and the Aztecs sensed that France was weak, so they attacked on both fronts and they took control of about half the French empire each.
On my continent, there was still 6 city-states, so I decided to mop them up to secure control before taking over the rest of the world. This triggers the city-states to ally against me, which was easy enough to deal with, and it allowed me to gain a foothold on the south-west of the Arabian continent. Once I captured the two city-states there, I declared war on Arabia, and captured the central city of Baghdad. Then came the scariest moment in the game as their massive army emerged from the fog and surrounded Baghdad, forcing me back to my city-state footholds. I was technologically much more advanced than them, I had cavalry and riflemen while they still had medieval units, but they outnumbered me and managed to destroy half my army before they ran out of units to throw at me. After that, my first tanks were arriving and I was able to take the rest of Arabia pretty swiftly.
Next on my list was Stockholm, the last city-state and positioned at the northern tip of the Persian continent, which was strategically vital as Persia had control of western France, so taking control of Stockholm would give me to perfect foothold from which to wipe them out. At this point, I had enough money coming in to upgrade all my tanks to modern armour, while the Persians were still in the process of upgrading their riflemen to infantry, so I didn't have too much difficulty taking them down. So, with only the Aztecs left, I positioned my armies to attack from the north and south, I surrounded them with my navy, and I prepared to win the game. Frankly, it was overkill because they were really backwards technologically, their most modern unit was a single cannon, so I hoped to wipe them out quickly. I declare war, I capture his most southern city and... crash to desktop.
That was a bit irritating, but I had a save before going to war, so I reloaded tried again and... crash to desktop.
Reload... crash to desktop.
I gave up, came back to it the next day, tried again and... complete system crash! My hard-drive had a stroke and the Windows bootloader was corrupted, I had to load the Windows disk and do a system restore to get the computer running again. I tried again two days later, managed to capture a city, I saved the game, and when I tried to move another unit, the game crashed. I tried to load that save, but it was corrupted and wouldn't load.
So I looked it up online, and it seems that the moment you capture or build your 70th city, the game crashes, but if it doesn't crash and you manage to save the game, that save file is corrupted somehow. I don't know how the beta-testers didn't find this bug, because I encountered it on a standard map, on huge maps it's not uncommon to have over 70 cities.
Anyway, I went back to the game and raised some of the smaller cities I had conquered and then attacked the Aztecs with absolutely no trouble. I had to raise their cities instead of capturing them, which slowed down my advance because it could take up to 4 or 5 turns for a city to be raised, and I couldn't capture too many cities at a time. I saved their capital for last, nuked it just for fun, and won a domination victory.
Fun game, lots of bugs, needs a few months of patching to become a great game. It's a standard Firaxis release.