There are new mechanics in it although I'm not entirely sure what they all are so far. From a very brief glimpse so far, the government management appears different to C5. It has a card game (harking back to the board game I played back in the 80's) feel about it. I know there are changes to the way that the Hex resources and buildings work meaning you need to trade off production/food for the culture/building functions you want for your empire. But I haven't really got that far yet.
Graphically it was slick and a bit more cartoony than 5, but I like it so far.
It probably is very similar to Civ 5 but I have to admit that I am a "phanboi" of the series and owned almost all the versions so far - So I am about the subtle changes more than others