Have we reached the point where Glee's musical releases have become more significant than the show itself? Maybe not, but we're close. At the very least, the stand-alone songs certainly make more sense than a lot of the plots. Volume 4 boils Glee down to its essence: pure, poptimistic choral joy. Classics are treated venerably (Mercedes channels Tina Turner); current hits are improved upon (boys' choir seriously trumps Katy Perry); and Brittany does Britney! The highlight of this disc is Kevin McHale's Artie, whose considerable skills get some much-deserved spotlight here.