dragons and giants make fine immortals in my book, and so does the first wereskunk, the immortal mother of all wereskunk-kin, and the stinkiest of them all, the mere mention of her name is enough to nauseate a person, and is usually spoken of in euphemisms. in my book, the first werecreature of it's kind should afford a special status, but the converted victims should be far weaker and far more mortal.
i do have problems with immortals that breed like rabbits, like elves and goblins. i could live with elves being immortal, if a bit scarcer and awesomer, after all, immortality gives you enough time to train all your skills to legendary plus infinite, and i wouldn't mind immortal goblins as mischievous spirit-like creatures that live solitary lives in magical forests and old abandoned towers, that hoard treasures and murder unprepared travelers, but i cannot live without hordes of generic baddies to slaughter, and i cannot swallow the idea that a creature that exists to feed experience to my soldiers and raw materials to my bonecrafters of dubious ethics has the potential to live for a thousand years and watch the dawn and fall of ages
that all of this is based on personal opinions is obvious, and luckilly, generally very modable