Continuing their slow crawl toward middle age, Linkin Park opt for moody over metallic on A Thousand Suns, their fifth album.

A clear continuation of 2007’s Minutes to Midnight, A Thousand Suns also trades aggression for contemplation, burying the guitars under washes of chilly synthesizers -- a sound suited for a rap-metal band that no longer plays metal but hasn’t shaken off the angst, choosing to channel inward instead of outward.

So few rap-metal bands have chosen to embrace their age -- they fight against it, deepening their technical chops while recycling ideas -- that it’s easy to admire Linkin Park’s decision not to shy away from it, even if their mega-success gives them the luxury to pursue musical risks.

The problem is, the subdued rhythms, riffs, and raps of A Thousand Suns wind up monochromatic, an impression not erased by the brief bridges between songs, sampled speeches, and easy segues, every element retaining moodiness without offering distinction.

Brooding is a better vehicle for angst than rage for a group whose members are well into their thirties, but an album created on a grayscale is less than compelling for anybody lacking the patience to squint and discern the minute details.