by Stephen Thomas Erlewine   Since Mansun's debut album Attack of the Grey Lantern was some sort of convoluted song cycle, it shouldn't have been surprising that their second album, Six, felt like the second coming of prog rock. What was a surprise was the extent to which Mansun pushed the limits forward on the album. From the garish Marillion-styled artwork to the endlessly shifting, seguéd songs, Six fits into the grand tradition of prog rock, and it does tell some kind of a story, even if it's impossible to tell what that story may be. In fact, it's difficult to get into the music itself, even as it dazzles with its twists, turns, appropriations and recontextualizations. And, make no mistakes, Six is frequently dazzling, since Mansun skillfully melds classic prog and pop styles with contemporary ideas, including a healthy portion of electronica. It's a head-spinning listen, especially the first time through when it's impossible to tell where it's going or where it's going to end. That feeling doesn't quite let up on repeated listens, either, mainly because the record is so dense with impenetrable ideas -- ideas that are confounding even when you think you understand where Paul Draper is going with the entire thing. On one scale, that's an impressive achievement, but it's diminished somewhat when you take into account that Six isn't particularly rewarding once you get a handle on it. Since it never reveals its secrets, or even its clues, it's hard to embrace the record, even for all of its many attributes. Still, Six is clearly the work of ambitious, gifted musicians who aren't willing to stay still, which is reason enough to try to come to terms with it.