The game IS best when it is humans playing humans. Always.
No.
It's best when it's
people playing
people.
My current Eberron campaign has not a single human, and there aren't any of the racial stereotypes people tend to insist are nearly inevitable with non human characters.
The dwarf is a dragon blood sorcerer with slightly blue skin, who wanders around living off the land and peddling simple wares, repeating things, etc, other than a brief stint as a Cyran mercenary during the war.
The half-elf is the closest to a stereotype, because he is a bard, but he channels his magic via his Dragonmark (Storm), and focuses on being an epic storyteller, and expert swordsman and ship's pilot (now airship captain).
The elf is also close, being a druid, but she is neither a standard FR-style druid, nor a standard Eberron Elf. Her people have a whole thing with a vast library in the form of semi-aware trees that they tell their stories to, the whole stories of their lives and deeds, and the trees record them, and pass the stories to younger trees when they near death, and thus their ancestors are never truly lost.
The rest of the party is:
a Kobold Wizard on a revenge quest against the dragon who murdered his dragon mentor,
a Shadar-kai monk working as an inquisitive in Sharn and trying to get away from his past as a gladiator and mercenary,
a Vrylocka Paladin of The Blood of Vol whose ties to her family keep her grounded in spite of exile, and who is on the trail of a conspiracy that threatens her entire worldview,
a Kalashtar Mystic who is caught between a desire to stay one step ahead of the Inspired, and his impulse to help people,
a half-Drow Warlock whose "patron" is his patron ancestor, raised by the racist parents of his elves mother, who is searching for acceptance, and his half-Drow father. And for an explanation of how he has a patron ancestor and a Dragonmark when he is not a "proper" half-elf nor a "proper" elf,
And their NPC allies, where we finally get some humans.
Now, in a world with only humans, all the cultures and predjudices and such that inform these characters might work fine, but in Eberron the places of each race are carefully considered, and have to do with their origins, history, and unique nature. These characters are informed by their culture, but their culture is informed by their
nature.
In the case of the Kobold Wizard, he can't go to the library of Korranberg because the Gnomes there don't want a dirty Kobold in their great city, much less their precious library. That is a history and culture thing. He also speaks draconic and views himself as equal to anyone else, even the Dragons, because Kobolds in eberron believe they are the true children of the progenitor dragons. Again, you could do that with humans, but it loses nothing by being Kobolds and Gnomes.
Khalid, the Shadar-kai is interesting, in part, because he comes from Thelanis, Eberron's Feywild, in a region that is more like the Shadowfel(I don't use the 4e answer of putting shadowfel stuff in mabar or Dollurh), and bc he has to meditate to stay emotionally level, because his nature makes him too sensitive to stimuli. His history since coming to Eberron is also interesting, but a big part of his story is informed by his physical nature.
Which brings me to the next big point. The other races
are human, in the end. Not literally, but in the sense that they are social animals with the same fears and hopes and (most of) the same needs as your or me. The trick in playing non humans is to find the "humanity" in a character, and build from that, informed by the unique nature of the race, culture, and background that character concept brings to the table.
Lastly, DnD is best when it is used to allow us to challenge ourselves.
