Do you think this game should be full open world? or just instance based? Let me know some feed back

I don't think Instanced based would fit this game based on what I have seen. I suppose they could instance things like the Invasions and such, but then it wouldn't feel quite as immersive.

I think they should only use instances for specific things and leave the game as open world.

I think the more full open world it is the better.  One of the things I enjoy about MMO's is that open world feel.  It looks to be mostly instanced in terms of the majority of content though; especially high end content.