Music that all sounds the same, the we're-alternative-but-wear-the-same-uniforms, sensitive music that all sounds the same and the whole Celtic-as-Lifestyle nincompoopery.
Not to say there isn't something legitimate within Celtic culture and history.
It's just the bizarre American-style co-opting of an ancient and wondrous culture into a so-called "alternative" movement that's as much based on capitalist consumption and marketing as the world they are trying so desperately to pretend they aren't in.