So, here is my take on the issue:
1. The down time is way too high. The turns for the computer civs are not very fast. It often take a minute or more to wait for the computer players to finish their moves.
This would not be that bad if a human player had a lot of things to do on his/her turn. However,
2. The game is bordering on being a simulation. Most units/buildings take a long time to produce, which means most turns take 10-30 seconds (unless you are in the middle of a war), and then you need to wait for the next turn.
Since so many facets of the game have been "streamlined" or "dumbed-down" or "simplified"... there's really not much thinking required in order to manage your empire. You are really just checking for happiness and what building you need to produce... and then you wait... This means that a half-way decent player will make most of the same decisions as a good player given the same set of conditions... so, the game can be quite boring.
I agree that it is hard to keep the will to finish a game. I have known for over a day now that I have won the game... but it takes forever to finish things. The computer players are smarter, but they are not human-smart. They often know what I am thinking, but they don't know how to stop me. So, my army moves forward, capturing/liberating city after city. While I believe the new combat system is far superior, the AI can not consistently put up a good fight.
anyways, it takes a realllllly long time to feel marginally satisfied. I think this does need to be addressed.