@Jay
Yeah, I completly stopped playing C5. I first just wanted to give a try to C4, having read all those complaints on this forum and willing to make my own view. It took some hours but I finally got hooked by C4, more than C5.
There are two sets of reasons for this, the first (but the one of least importance in my decision) being the lack of polishment of the game, software-speaking : tons of bugs, turns sometimes taking ages to end and adding to the emptiness feeling of the game, broken features (general IA, diplomacy).
The second was summarized on this forum as the dead of the "one more turn" feeling.
Here is the highly subjective part : one cannot demonstrate which is better between rushing building or just buying them, doing transports or just embarking, loving C4's civics or C5's policy system. But in average I love C4 better.
My personal feeling is that there are not so much things to do in C5, choices aren't that important (tech order, city placement,...), the enjoyment per turn being lowered and, given the length of turns, the enjoyment per minute having drowned^^.
I think this is not only a result of some lack of features compared to C4 (which is real, but not SO HUGE, and I will not spend ten paragraphs whining on the death of religions that nicely intricated diplomacy, gold and culture, and other feats) : most of the feats are there, but you just don't use them.
IMHO it's more a consequence of the non-existence of AI, which turns the game into a warmongering shooting feast that is the same in every game I created after the first ones where I took time to discover the mechanics. 1 upt is really great, but the IA don't get it.
So in every game I end up founding only 1 to 3 cities, puppetting the rest of the world while getting huge amouts of science and gold for this, and having medium culture production but low new policies costs and thus being able to go for any victory type.
In addition, a feeling of playing alone in the middle of brainless bots in a soulless game due to the lack of a true diplo system.
Of course, the game will probably be wargame-oriented in MP too, but it should be more interesting.
In a few words, less feats, no IA, one way to play, less immersion, lots of bugs. That's what I discovered about C5 trying C4, and will stick to the latter unless a major update shows up (but, more realistic, this will probably need a full expansion).