I find active cancelling headphones to be very unpleasant. I've switched to custom molded in-ear monitors which do an even better job of eliminating external sound (musicians wear them on-stage to protect their hearing), sound better, and don't bother me the way active cancelling earphones do.

I have no idea if active headphones are "bad", just that they make me feel very uneasy.

The downside is that Custom In Ear Monitors are pricy (> $1000). When you have them made, you can often choose how many db of ambient sound attenuation you want.