This volume in Ultra's high-energy (not high-NRG) series, mixed by the Riddler and Trevor Simpson (each gets a disc), continues the Ultra Dance formula of a first disc largely composed of club mixes of pop hits, while the second goes a bit more underground, or at least less poppy. In practice this amounts to the Riddler getting tracks by Christina Aguilera, the Killers, Rihanna, and Panic at the Disco to play with, while Simpson puts the likes of Sunloverz, Tom Novy, Eric Prydz, and Sander Kleinenberg on his turntables (or, more likely, his laptop). In this case, it also amounts to the Riddler having the better disc, thanks less to his mixing abilities (which are fine, but nothing extraordinary) than to the mostly sterling selection of cuts he gets to play (with). "Opsina Sullivan's Club Mix" of Aguilera's "Ain't No Other Man," which opens the proceedings, is a near-perfect mix of chunky big-room house and pop sensibilities, while Chris Cox offers up a sterling take on Rihanna's overplayed "SOS," wisely leaving room for a full-on "Tainted Love" breakdown mid-song (the former is based around a loop from the latter). Simpson's disc has its tasty moments as well, foremost among them Seamus Haji's "Big Love Club Mix" of Booty Luv "Boogie 2Nite" (a fun, funky remake of a Tweet song, and rightfully a huge hit in the U.K.), but he gets a bit strung up by a brace of tech-trance numbers as his disc goes on -- they're mostly fine, but get a bit samey. On the whole, though, this is a solid selection of big-room tunes for reliving those lost Saturday nights -- or inventing them.