I'm a big CKII fan and I didn't like EUIII at all but I have preordered EUIV. From watching the quill and dev videos you can tell that they have made great strides in making the game more user friendly and enjoyable without dumbing it down to the level of something like civ5. The biggest thing is that you now don't have to navigate a maze first for the game to be fun. As someone who has played CKII a lot I am sure you know that the game is fun with only a basic understanding of the key systems. You don't need to know how to be gamey and exploit everything to enjoy it and that is the direction they have put EU on.
It is sandboxy like CKII but in different ways. Instead of roleplaying your dynasty to complete personal objectives you can choose to go different tech routes for your country as role playing. Being a power with naval, land, trade, colonization, and being offensive or defensively minded. I would recommend buying it since it looks good from the previews and it will be very different from CKII but similar in enough ways that you will probably like it. They will probably have a demo out for it before release but I don't know how much you will really learn from that when these are games you need to invest time in to really enjoy.