I very strongly favor the idea of each race having its own very different advantage and disadvantages, rather than each race just having its own cosmetically different version of adamantine. More complicated and difficult to balance, yes, but much more enjoyable results.
Dwarves: long-lived, tough, superb mining and smithing abilities, extensive steel production, access to vast mineral resources (sometimes including adamantine), nigh-impenetrable underground fortresses laced with clever mechanical defenses, mounted war-bear cavalry, maybe some sort of runic magic or whatever once that's implemented. On the other hand, somewhat reclusive, on the small side, susceptible to cave adaptation, FREAKING CRAZY PSYCHOLOGY, and somewhat slow to reproduce.
Elves: VERY long-lived, rather high initial skills due to longevity (especially ambush, bowyer, archer), good memory so skills don't "rust," can survive and even thrive in any "natural" environment (I'd love to see desert elves as in Battle for Wesnoth, sea elves, maybe even mountain elves), have powerful animal allies (maybe even riding into battle on unicorns and griffins and the like), nature-themed magic once it's implemented, overwhelmingly fast-firing elite archery squadrons. On the other hand, somewhat shunned by other races due to cannibalism and disdain for city folk, very slow to reproduce, complete lack of metal (although hardened wood about on par with iron would certainly be reasonable).
Humans: innovative and flexible in ways that the Older Races find difficult to understand, faster reproduction rate, well-organized due to city life, widespread civilization, aggressive and confident, excellent balance of industrial and agricultural capabilities that can both feed and arm large armies, fast and hard-hitting horse cavalry, reasonable diplomatic relations with most other races. On the other hand, relatively short-lived compared to Elves and Dwarves, typically less skilled, seen as somewhat "new" on the scene, less magical ability apart from the occasional powerful sorcerer.
Goblins: small, weak, and often poorly armed, but there are LOTS of them, they're vicious, very well-organized in battle, accompanied by trolls to bash down doors, and often led by powerful demons or sorcerers with dark magic to back them up.
Kobolds: small, weak, primitive, but very sneaky, and cute too! I don't know; maybe give them a poisonous bite or a mutant healing factor or something; I almost feel sorry for the little guys. I guess kobolds don't really seem like they need to be balanced in the same way as the other races; I don't really see them as the sort that are going to be attacking the fortress as a huge army so much as sneaking in as single spies or small gangs to scout, steal, or sabotage. Heck, maybe they could sell information or stolen artifacts to the goblins. I would imagine that playing as kobolds wouldn't be so much managing a kobold cavern (do kobold caverns even have managers?) as controlling a squadron of kobolds infiltrating some other civilization to accomplish some mission. (Anyone here play Kobolds Ate My Baby?)