As others have already said, it doesn't feel complete when compared to Civ V with 2 expansions. Perhaps that's not a fair comparison, but after playing two games of BE, I'm ready to play Civ V until BE gets a few more expansions.
Some of the new elements are neat, but need to be reworked. It was a bad idea to implement the optional functions of each building as quests. It's confusing, and makes it difficult to plan ahead. Overall, quests are just poorly implemented. Most of them are simply associated with doing what you would normally do in a Civ game. In the future, options for buildings should be separated from interactions with other players.
The tech web is also really confusing. They need to make it easier for decisions to be made at a glance, and make it clearer what research leads to what benefit. I get that it's impossible to make research as intuitive as it is in history-based Civ games, but there has got to be a way to improve it so that I can look at a tech and know that it's going to help me improve my civ's health, or power generation, or whatever. So far, I spend way too much time trying to navigate the web to figure out what branch grants me a certain benefit.