When Helmet first burst onto the scene in 1991, they were a brutally relentless assault on the senses. With each passing album, however, the band became more polished and more melodic. You know, more like every other hard-rock group out there. Not surprisingly, the ''reunion'' CD Size Matters (frontman Page Hamilton is the only returning original member) is an occasionally catchy but ultimately bland attempt at recapturing past glory. Size may matter, but when it comes to Helmet, so does unfiltered aggression.