Unbelievable finds Diamond Rio extending the stylistic diversity that marked IV, but this time around, they have a better, more memorable set of songs that makes it their best album in a long time. Diamond Rio are professionals, and that's part of their charm. They can deliver any song smoothly, and make their musical eclecticism easy to swallow. Also, Marty Roe's rich, nuanced vocals make the mediocre material (and there are a couple of weak cuts here and there) sound sweet. It's not perfect, but Unbelievable nevertheless offers proof that Diamond Rio has found a near-irresistible mix of contemporary country and bluegrass.