My 4b fortress is now 5 years old, and I felt like sharing some thoughts. First off, the libraries.
While I like the new system more than the old one, I think it's still more trouble than it's worth currently.
The reagents are simple and not hard to get, that much is true. But it still takes a while to produce enough jugs, ink, paper / papyrus and glue to write enough books for even one library. The problem is, by the time all that is done, my dwarves are too skilled to make use of the libraries.
Early game, there are much more useful things to focus your dwarfpower on, and later on, you don't get much use of the libraries. I only used the libraries in two cases:
1) I needed a new farmer / smith, so I'd bump up a few of his skills
2) I had no dwarves naturally skilled in medicine, so I trained two of them in all the doctor profs
Most skills you really don't need on more than one or two dwarves, and lvl 4 doesn't take long to achieve, even with Harder Learning on - so unless you're starting a whole new industry you haven't used before, libraries won't help you much with those.
Also, the process of creating the books for a particular library is a pain. I appreciate the flavor names of the books, but it's annoying to have to either write down all the names you need, or have to jump between the library and the manager repeatedly to queue up all the needed ones.
So long story short - I felt they still aren't useful enough to warrant the effort required to create them. The system itself I like, it's just the balancing that is a little off, in my opinion. What do you guys think?
Secondly, the tree-farming - specifically, the ironbark and steeloak trees.
Since the Sawmill is now so easy and simple to build, I don't even bother looking for hematite anymore. Two sawmills, one 8x8 farming plot for each tree, and soon enough you find yourself with a limitless supply of iron and steel. You need to research the Herbalist, true, but the reagents for that are very simple and quick to gather. Stick the "cultivate iron / steel" processes on repeat with workflow and you'll never ever need to think about it again. Some may argue it's just un-dwarfy to make these sacred metals out of trees, but then an elf diplomat arrives to complain about the deforestation, and it just feels SO GOOD to stab him with a sword made from a steeloak.
It's true that with hematite, you can also workflow your way into completely automating the process, but it's both way longer (for steel, at least), and you'll eventually need to do some mining to find new veins. So I think the trees should be nerfed in some way, not sure how though... perhaps make them take even longer to grow, or make the Sawmill harder to build?
I think these are my only complaints so far. Loving the new magic system, even though it's expensive as heck, and despite a migrant flamemancer burning the surface part of my fort to the ground (having decided to fireball a Giant Hornet Queen in the face while carrying some trash outside...). I need to check out the Colosseum soon, my golem / mage army needs a new challenge