Because I'm bored,
I've decided to sort of catalog some of the ways in which the new embark screen and mineral distributions (and other resource availability issues) are causing people problems or frustration, potential reasons for those issues, and possible solutions. This way, there's at least sort of a rundown in one location, as opposed to retyping various bits of it all over the place. This is sort of for everybody's benefit, including the people miffed by how things have changed, just to make it easier to think about these changes, what they mean, and how things might go in the near future.
- Parent civilizations tend to be lacking in available resources. We have reports of lots of cases where dwarves can't even embark with iron or steel. This is possibly because of problems tracking site/civ resources, or possibly because civilizations are not smart about choosing where they expand and build new sites. In the latter case, civilizations should attempt to expand to locations containing resources they know they're missing; there's no excuse for dwarves going 150 years without finding some sources of iron and copper and building sites there. There's also no real excuse for your starting dwarves not knowing what's available from their civilization pre-embark, preferably when you choose your civ.
- What minerals exist on your site is far too difficult to determine. It's understandable that we don't have or need the old layer count anymore. However, it would be both realistic (enough) and less frustrating for people if the major deposits on a site were identified, such as iron, or copper, or coal, as well as possibly (but less importantly) the general classification of rock (e.g. igneous extrusive, sedimentary) near the surface, as this is stuff that isn't unreasonable to know, and prevents people from scumming constantly just to embark on an iron vein. After all, wanting to found an iron-smithing or coal-mining fortress is completely valid, and there's no huge reason we shouldn't be able to have access to some of that information (after all, how does it make sense that we know that metal and flux exist somewhere, but not that the top layer of the place is sedimentary, or that the metal is iron?). For that matter, it would be nice to treat other valuable non-metal resources such as coal, sand, kaolinite, and whatever else is useful but not tracked here, as if they're worth mentioning.
- Trade is not robust enough to supply the player with what he does not have. Evidently, the goal is for sites to have more of a signature to them and be less "all-purpose", e.g. less of the "everything is everywhere" approach and more focus on larger deposits of fewer resources, so that trade of those resources between sites matters. However, without the trade to back that up, players are left in sort of a sticky situation, having to rely on fairly unreliable and small caravans for major resources.
- The world just plain doesn't have enough mineral wealth. This is somewhat speculative on my part since I'm relying on what other people are telling me and I'm not sure how much is known here, but it's possible that too much of the world is simply barren in terms of mineral wealth. If this is the case, it's no wonder that civs and fortresses are lacking in these things, but it would probably also be relatively simple to adjust compared to the other things mentioned here.
- The relative scarcity of some resources is off. Probably owing to the lack of adjustments to how veins work (so this may be fixed soon), I have heard that extremely valuable and rare metals like platinum can constitute very, very large deposits. Now, large gold mines aren't that strange, I suppose, but for things that are meant to be rare to the point that you're lucky to ever find some, like aluminum and platinum, it's pretty important to make sure they're actually as rare as they should be. In fact, when veins get adjusted, it might be worth going over minerals in general and breaking away from the old vein/cluster system, so that we can have things like realistic coal mines/layers, extremely rare platinum, kimberlite pipes in volcanic areas, and whatever else is deemed fun/realistic/necessary.
- Inertia. Players are used to having a lot of materials and their sites being self-sufficient. Moving away from this paradigm and towards a better long-term one is fine, but people are shaken up by this level of change, especially when they're stuck in this state of limbo where the change looks bad because it isn't complete enough to be as viable as what we had before. Obviously, the only solution to that at this point is to keep on trucking and get those other features in, or, if necessary, tone down the lack of minerals until the game has the infrastructure to support it better.
That's all I can think of at the moment. There's probably more, but that's all I have rattling around in my head right now.
I'm aware that at least some of this has been considered for far longer than this release has been out, but it's still worthwhile, I think, to examine what's going on just so it's more clear to everyone.
[edit]
Added two points and added a small bit about non-metal resources to the point about the embark screen/mineral randomness.