A sign of good concept album: removing the concept from the lyrics would weaken the album significantly. I don't feel that the concept adds a ton to MAYH or Still Life. Change the lyrics, and these are pretty much just as good. These are just albums that tell a story.
An album like Dream Theater - Scenes From a Memory really is a good example of how outstanding a concept album can be. It's really, really good, despite all the fanboys and losers who gush over this.