"Aliens" Who Aren't Human

Just finished The Mote In God's Eye, by Larry Niven and Jerry Pournelle, and it got me thinking. In most fantasy settings, humans are typically represented as the shortest-lived but most adaptable of the species. However, the non-human species, with few exceptions, are basically human with little reason why they would not also be every bit as adaptable and generalized.

Bear with me here. It seems a reasonable assumption that any intelligent, tool-using species that developed with a non-segregated species would be a generalist, which means adaptable but non-excelling. And that's boring as shit, because humans already fit that niche.

My point?

I think it would be far more interesting to have a non-human species be different than humans, rather than longer- or shorter-lived versions of humans.

Brief summary for myself - The Moties have short lifespans and definitive segregation within the species. All species except cross-caste mules go through male and female phases (I think male youth, then female, then male elder). They suffer excessive population pressure because if they do not breed during their female phase, they die quite quickly (months to years?). All castes have fairly short lives, 25 to 50. Their only viable birth control renders them sterile as well as shortening their lifespans (though not as short as failing to breed) - also, the birth control only works if applied before they breed. Hmm... what else. Ah. The species segregation of the Moties is due to mutations creeping into the genetic post-atomic war, which were encouraged into viable specializations.

Okay, I'm not sure that I'd want to use a species exactly like the Moties, either in fantasy or sci-fi, but at least stepping outside of the generalist stereotype might provide some variety. In fantasy settings, humans are almost always the dominant species because of their adaptability and breeding rate. However, the other races are also generalist (or if they are not, there is no explanation why) and generally longer lived. I'm not really sure why they wouldn't be the dominant species - longer to learn skills, capable of developing skills that shorter-lived people would simply not have time for.

Right, so, rambling without getting anywhere. Still, good theoretical thoughts, might be able to apply them later.