Beyond lycanthropy, can you use Detect Magic to sense an animated skeleton? A doppleganger? A vampire? A summoned creature? A golem? A dragon? A polymorphed gold dragon disguising as a human? I'd probably allow it for the skeleton (if it had been animated by a spell), the golem, the summoned monster and the polymorphed dragon, but probably not for the others, unless they had active spells on them. Couldn't use a Detect Magic to root out a doppleganger, for example. But that isn't backed by anything other than gut feeling and a sense to preserve certain story tropes.