Changes to minerals:
Occurance and abundance are rebalanced based on the Minerals Mods by Sean Mirrsen, and on additional research in
http://rruff.geo.arizona.edu/doclib/hom/, wikipedia and the sites linked from its articles, mindat.org, and a number of specialty sites for particular metals and gemstones.
Every mineral is economically important, or valuable, or colorful, or serves as a matrix for inclusions that are at least one of these things. No more "magnetite feast or microcline famine"! Every fort will have more diverse metals and colored rocks. You may easily see half a dozen different cluster types on a 3x3 map, and every one may host important ores, valuable decorative minerals, or beautiful gemstones. You might unearth iron-bearing pyrite and crystals of calcite in mica, or come upon a granite cluster with tin-bearing stannite in a diorite layer, or get really lucky and discover a chalcopyrite lode with molybdenite or a native silver vein with kelshinral.
It is more practicable to play on maps without magma because coal is both more common and more productive. You don't need to search nearly so hard for sites with flux, because you're likely to find at least some flux at more sites. All soils are sand - apply whatever house rules you like.
Valuable and colorful decorative rocks encourage creativity in furniture and furnishings. A throne room with pillars of Jade, Turquoise, or Lapis Lazuli is quite valuable!
Changes to metals:
Lots of new metals, many based on Sean Mirrsen's work. Lamshinral (silvershine), Mirrorsteel, Isrirkadenkel, Athamadagi, Blueshine, Gorroth-kel, and Patterned (Wootz) steel are all both more difficult and more rewarding to make than the standard metals in the official game.
Every metal from the standard game is changed. If it was boring and couldn't be made interesting, it's gone. If it needed a coolness boost, it got one. If it needed some rebalancing, that happened - usually over and over again until things finally looked good!
Iron-making is somewhat more costly and iron ores are worth a lot less, bronze is stronger (now roughly equal to iron), and gold (not platinum) is the premier noble metal. You can only make alloys using bars, but simple alloys with low melting points require no additional fuel to make. This makes brass and bronze attractive options on maps without magma.
Changes to gems:
About half the gems are gone, including 12 out of 15 types of opals. All of the rest are sorted into easy-to-understand categories, many are more valuable, and some new natural gemstones are now on offer. Rock crystals are easier to find.
Miscellaneous changes:
Mineral and metal tile colors are altered to make them easier to tell apart, or more realistic, or just prettier. Several of the color and tile changes are from LordZorintrhox's DwarfLetter tileset/mod, but they're all intended for use with a tileset of your choice.
As in the Legendary Lands mod, edible plant products are worth less in comparison to metals and gemstones than in the official game. Unlike in that mod, this is accompished not by raising prices, but by lowering them: cookable plant products, Dwarven Syrup in particular, are worth less. Same story with raw ores versus smelted metals.