This game needs more randomness and more events. By that I mean that, more often than not, "historical" superpowers tend to get the best colonies, more tech,... I wish that you could have random big plagues, social revolutions, large countries being ripped apart, genius leaders leading a second-rate country to glory, etc...
More sliders, decisions too. What makes this game great is the depth of it. What if I wanted to force women to stay home and have many babies? Or if I let them join the army? What if I created my own religion to suit my political needs? What if I outlawed religion? What if I decided to ban a certain culture?
Actually, I'd love an expansion to let the player choose between an intentionally ahistorical alternative world AND a properly historical game. I mean, the current game seems a bit stranded "somewhere in the middle" that can't be satisfying to those who prefer one extreme or another. While maintaining the current middle-of-the-road game, adding a more strictly deterministic historical game and a random chaos game would finally satisfy both the history buffs and those who want to say screw history.
And by the ahistorical alternative world, I mean much more randomness that the in-game history takes decidedly strange turns and that is to be expected: Novgorod storms the Russia! Ulm turns monarchy and seizes the Imperial throne! Ceylon proclaims the return of Buddhism in India! Aztecs swarm to Lisbon! Just softening the tech group gaps, boosting the "lucky nations" bonus even further and making different AI nations "lucky" every 10 years or so could certainly create a huge chaos, right? You, France, thought you could finally finish off Brittany and suddenly it becomes lucky and spawns god-generals and slaughters your entire army... in a way, this is the stuff of the epic poetry in the real world, ain't it?