I've played Morrowind and Oblivion countless times. And honestly, I've always thought that their race selection, while awesome was still very limited and based mostly on standard fantasy cichés.
Your humans are pretty obviously based on. Vikings,Celts, Romans and Africans with vague allusions to mysterious asian-based "Akivir" and no acknowledgement whatsoever of native american (as in any from all across north & south america) or eastern european cultures or races. Your elves are the standard high elf, wood elf & dark elf combination seen in every fantasy story since Tolkien. Orcs take the traditional place of dwarves in order to make them less evil and more playable. And then you get lizardmen. Another fantasy standard. And then Catmen are added. The cat people are the most original race in the entire selection of playable race. I mean half the time I'd rather play as a daedra than any of the 10 you can play as.
However, I agree 100% that the playable races' histories and cultures within the game are extremely well thought out and it does make everything more fun to play. But I wouldn't exactly call them different from most fantasy races.
And Rune, your race is very cool. I love what you've got going with them and think that the other humanoid races would benefit from being as unique and detailed.
Now, I haven't created the Dragons yet, partially because I want to give them a more complex culture than just being Big Bad Monsters. And I'm not doing so well with getting my thoughts together on that.
But the way I see it we have at least a few options for adding races and cultures into the world. Two ideas I just thought of:
One thing we can do is, once our races are created outline different subspecies that the will evolve into.
We could also try to have everyone come up with at least an idea for another humanoid race & their major culture(s).