Unless you're writing the spawn of Lionel Shriver's We Need to Talk about Kevin, odds are you're going to want your readers to engage with your characters. They may not like them, they may not agree with them, and if they're anything like me they might want to strangle them on occasion, but a reader who is interested in and engages with a character is a much happier reader than one who's counting the number of pages until they can put the book down and never look at it again.
But what makes a character engaging? There's no set formula for that, mainly due to the wide variety of readers in the world, and what each of them likes best.
However, if you want a reader to engage with your character, they're going to have to be one thing: human.
Right? Not neccessarily.
To be fair, the majority of main characters (who, in turn, make up the bulk of narrators, thus doubling their importance) are human, or humanoid at least. Even in the wildest of science-fiction novels, odds are you won't be following the story of the tribe of forest-dwelling orange platypi, you'll be following the rather confused cosmonaut whose ship seems to be forming the bulk of their mid-day snack.
And why is this? Because being human makes a character that bit more approachable in the early stages of a story. You might swap to the perspective of the half-platypi outsider a bit later on, but if you started off a chapter listing her concerns over the size of her beak, her lack of flippers and inability to make a graceful entrance to the best mud spots, the reader might feel the distance between them is too much, and will flip over to reading something else.
However, I disagree with this. Why? Because I think it's not the external humanity that counts, but the internal.
There are innumerable situations that can arise out of the tiniest action, and accordint to emotivists, we react in certain ways because of primordial emotional responses. Why should it make a difference if our emotive response is towards someone helping an old woman across the street, or from a tiny platypus-beast doing just the same thing.
With narrators, I'd say we have room to be far more flexible; whether third person or first, we are going to spend the story following their thoughts and actions, and we are going to see their personality through that. The situations might be strange, extraordinary or bizarre, and the lingo might take a chapter or two to get around, but in the end it, engaging with a character all comes down to us, and them. They might be brave, timid, cautious, inventive, proud, a great leader, a canny traitor - and in the end, whether they have two legs or twelve isn't going to make much of a difference to our view of them.
To me, as long as a reader can engage with the thoughts and personality of the main character, their species shouldn't matter.
And hey, being non-human can even be attractive in a character. Let's face it, we all know how boring it is to be limited to our ground-bound, squishy-bodied existence, and I've always found something incredibly fascinating in narratives where the we can see the subtle differences in how a non-human character conducts themself in a given environment, either through the customs of their species, or through automatic responses to circumstancial change.
We know we're not supposed to judge books by their covers. Let's not judge characters that way either.
~ Charley R