So far, it seems pretty cool. Here's my thoughts -
First of all, the rewards are actually pretty good, even if it may take months to get them at their highest levels. The emissaries making the space taken by your town hall less "wasted" is pretty great, for example.
I see a lot of feedback about this being just a way to get people to spend diamonds. As far as I was aware, though I'm sure Inno's developers actually have a love for city building strategy games, the aim of everything they do is to get people to spend diamonds, so why would this be different?
That said, I don't so far see anything that makes it so that you NEED to use diamonds for this. Of course it will speed things up, but saying that is so incredibly redundant when you're talking about any freemium game.
To me, its a pretty cool puzzle that is a side/minigame. It's slow moving for sure - but that's fine cos it's not the main event - it's something that should just take up a little of your time, but fairly regularly so you have something to do between having finished GE on a Thursday afternoon and whatever the next event is. At least, that seems to be the goal here, along with providing fresh content to all users, rather than just those at the end of the tech tree.
I do think that it probably appeals more to folks who have a "farmer" vs a "fighter" mentality. I tend to walk the line between both of those, veering one way or the other based on mood and the task at hand. For a farmer, optimizing production with constrained resources to maximize output - which is totally what the whole Vikings cultural settlement is about - is probably their cup of tea. There's really only one basic goal as far as I can see - produce about 950 cultural goods as quickly as possible. I think it would be awesome if future cultural settlements perhaps had a more combat-centric focus. I imagine culture specific units and barracks instead of as much focus on production buildings, with a mini-cmap or something like that.
While talking about the farmer vs fighter thing I have to point out that this new feature feels like a huge gift to two groups of people - campers and those who can't get past being plundered. First of all, this is available to everyone, regardless of age once you're in IA, with nothing that forces further tech development or c-map progress. Second, your settlement is not plunderable, and both of the special buildings are motivated, and thus not plunderable either.
So overall the new feature isn't hugely exciting and something so different that it'd make me go "wow". It seems in line with what FoE is though, and probably has a lot of growth opportunities as more civilizations are released. As someone who generally likes the game a whole lot, I (so far) like this too.