I think the units are way too large compared with the environment.
Furthermore, their movements don't look good. Have you seem them "hopping" forward?
Next, I don't like that still each battle seems to be lethal for one unit.
Next, I don't have seen any stacked combat. Together with the information about armies would have gone, this would mark a definitive step backwards
Next, I don't see how the graphical presentation of stacked units should work now. Imagine a stack of 1 sword (3 units), 2 spears (2*3 units), 1 crossbow (2 units after battle) and 1 horse... how would you be able to identify who is who?
Next (already mentioned), mountains just look bad.
I am not convinced of the line of sight idea, either. Of course, I haven't seen it in the game, yet, but it seems funny to have the chance to see city surroundings on the other edge of the world.
By mentioning the missionars and spys, I got the impression that it might be even more unit-based than Civ3 - leading directly into another micromanagement mess (m³ (tm)

)
Somebody already mentioned the icon-oriented display of what seems to be the new civilopedia. How to put in new elements (in particular, new improvements) when you miss the appropriate icon? Currently, you just can do a alphanumeric search...
After all, the graphical interface doesn't look very promising to me. It seems to be made for kids - a lot of moving items, but low content. In turn, this seems to indicate less strategy, in the worst case even less tactics... but full usage of the CPU and graphics card.