I'll be surprised if "Boring Endgame" doesn't win. Dumb AI is silly, but not game-killing for me because I can play with settings and mods and personal challenges to amp things up, but boring endgame is always boring endgame.
A few things I've been thinking about in regards to this problem:
1. Remember the break-away empires from Civ 4? They were a pain in the ass. They were also realistic considering the history of oversea colonization. I feel like the game does a good job of settling, expansion, consolidation, and warfare - which makes for an interesting beginning and middle, but when you look at the history of earth, what you see is something Civ sorely needs: an endgame that goes haywire:
- England lost most of her possessions to independence movements, the Soviet Union dissolved - why is empire cohesion so easy in Civ? I want big empires (that have benefitted from their sizes most of the game for production, resources, etc.) to break down. Not FLIPPING (which I found to be a pain), but becoming independent city-states, or (better) new emergent civilizations. The further from your captial, the more culture you have to generate to keep them. (A much better check than the penalty to culture right now.) Some people want Canada in the game, others object, but acknowledging that countries like Canada DO emerge is important. And having this in-game would be amazing.
- Countries like Senegal, Indonesia, were able to emerge from colonialism (somewhat spoiled in the case of Zimbabwe, etc., but independent nonetheless). How about cities that we conquer from, say, 1600 AD on, eventually mount independence movements as the World Congress begins convening?
2. I watched a video for Europa Universalis IV yesterday, and just that brief glimpse into that game made me long for more diplomatic and policy systems than what civ has right now, and for new systems in general. I don't know what those could be (still haven't played EU4 because my specs are bad), but just mine some ideas from EU4 and various board games (which are great at implementing systems). As the game wears on, there should be new challenges to face. I think tourism/artifacts was a HUGE step in the right direction. We just need more steps like that.
3. I want more victory conditions: how about religion (something like Islamic pan-Arabism) happiness, military influence (as opposed to domination - so you would have military in different spheres for influence without having to conquer), economic/corporate.
4. Random events in the late game. This should include quests. Not city-state quests, but other quests that are further reaching that would influence your decisions late game (got this idea from EU4).
5. In opposition to #3, what about a version with NO win conditions? (Got this from EU4). Have a thousand different accomplishments and quests that have nothing to do with size, and have to do with informing your play style. And make them interesting.
6. We have more Civs than ever before, but I want the Civs to have more civ-specific features within each civ. More complex UAs, 5 Unique U/GP/B/I each.
7. deleted because it had nothign to do with endgame
8. Cities need to become more interesting. That won't work for Civ 5, but maybe in the future. What if you have a little dash of SimCity in city management? More (smaller) hexes that you have less direct control over, but that have more interesting gameplay with the city to make city management interesting late game instead of time-consuming drudgery.)
9. It's time to make barbarians more interesting late game. Any gaps in the map should eventually emerge as city-states.
10. Which brings me to city-states. They are an amazing addition to the game, but now that we have them, I want them to be bigger and better. I think the one city restriction is actually a good idea (representing minor powers like Singapore), but the whole game need a bit more complexity, and city-states should rise with the tide.
11. When civs are marginalized on the map, relegated to no victory at all, why can't they attempt to merge? Sort of like the European Union, but united enough to mount a challenge to the 1-3 runaway leaders.