Oh, I know why they moved to Unity 5, but they seem to have put a lot of effort into redoing lighting, colors, and even design... You can literally see that some of the details look different, i.e. were redrawn. Windows that were previously dark in Mercuria are now illuminated. Hair styles sometimes different. Trees are different. Is this a trivial consequence of moving to a new engine?
Like I said above...basically yes. Ragnar mentioned that the artists are the ones with the most work to do in this port and that is largely because light maps, shaders, textures and even models in some cases needed to be tweaked or redone to work with the new system.
I don't...fully understand everything, but at least with the lighting, the gist that I've gotten is that U5 handles a lot of things very differently than U4 and some features that were previously being used no longer exist or are very different.
Some of the details that are different I think are not necessarily the result of something being completely redrawn, but may be the result of remapping and/or just details looking different because of shifts in light and shading. Like inside of the Journeyman I really don't think it's so much that a ton of detail was added in certain places. It's just that it was very hard to make out before.
I'm sure some assets are requiring a decent amount of retooling, but based on everything the team has said, they're not doing that because they wanted to completely rebuild assets or make visual changes. It's because the port ended up mucking up a lot more of that stuff than they hoped and they have to sort all of that out.
(Rikke/Mulm has actually vented some frustration about all of this on Twitter.)