The issue many of us have, is that the walls lack depth.
If you played PlanCo, you may have noticed that the default walls look kind of bare if placed, even though a real building from the same materials does. You have to place ridicoulus amounts of details on a single building to give it some character and get rid of that bare look. And Rookburgh seems to suffer from the same problems (please keep in mind that there are more pictures floating around than just the ones from outside).
It's surrounded by huge walls, but those walls tend to look kind of blend. Yes, the bricks give them a little bit, but it is not enough to make such a big wall feel natural. Klugheim and Chiapas were able to avoid this issue with their rockwork, especially Klugheim features an enormous amount of depths due to the shape and size of the rocks. You don't have this in Rookburgh, but only Brickwalls. They tried with some buildings on ground level, but those are quite small compared to the walls.
In addition, the basic shape of the walls feels unnatural. If you imagine a factory, you imagine a simple rectangular building with some smaller ones next to it - but only simple shapes for maximum use of space. No "fancy" 30° angles in the same building, or extentions for more than a staircase. What they could have done to solve this issue - we do know that the footprint of the walls was necessary the way it is, would be to make it look like it were multiple buildings, cramped together.
Parts of the wall look good, especially the glass "tower" in one part - it looks really good in person, and adds so much to the whole structure. But that's only one part of this encasement. The area around the hotel should be fine as well, as the buildings of the hotel add lots of depths to the area; if the back of the rusty wall is not as ugly as the front.
Ah yes, the rusty wall. I think that most people have the same issues with it as I do. It is neither good looking, nor inconspicous. What do I mean with it? If you build a wall which is visible from the outside, you basicly have 2 choices what to make it look like. Either make it inconspicious, so quite blend and boring, so no one will look at it for longer than a second. That's what the outside walls of most parks I've been too look like, and Phantasialand did the same in many places. Even the back of Klugheim is quite boring, and we are talking of a height of nearly 30m (~90ft). You won't overlook it, but you are not particulary drawn to it either - even though I'd given it a paintjob to make it stand out less.
The other option would be to make it look good and impressive, like parts of the hotel look like, or the area with the furnace next to the rusty wall. The rusty wall is meant to be seen, hence why the plantings, the signs and the lighting. They want you to look at it. And I don't know about you, but if I'd been asked to design an entrance for a highly detailed hotel inside a highly detailed area, I would have gone with more than a blank rusty wall with a pimple on it. It does not look inviting at all. The whole situation is made worse by the buildings next door. On the left handside, the good looking wall with it's furnace, and to it's right, the old building with an ugly "rusty" paintjob.
One more thing: One thing I noticed when standing in front of the "pretty wall" next to the rusty one: It also manages to look blend and unnatural if you stand in front of it. The reason is quite simple:
a) the windows are glass, but there is nothing behind it. It looks like a pane of glass in front of a blank wall. You instantly see, that those are not real
b) the metal strips on the wall and furnance are made of concrete - and that is quite obvious. They do not look like metal at all. You can see the red paint shining through in places, in addition to the concrete texture. Phantasialand tends to cut corners in places, and this is one of those situations. I don't think that real metal strips would have been much more expensive, but they would make the whole thing feel realistic. If you stand next to it, it just looks fake, which is a shame, because the bricks themselves look amazing.
Of course, in the end the inside of this area is what counts. But compared to Klugheim with it's handcrafted wooden buildings, highly detailed rock- and brickwork, it appears to be quite blend as of now. And that's the only thing we can judge right now: It's current state. And that raises some concerns in my mind.