Circus, Britney Spears’ sixth studio album, is a supremely satisfying dance record, stylistically cut from the same cloth as last year’s (also excellent) Blackout. Both are jammed with top-tier, glossy electro-pop songs. There are some missteps: The inclusion of “Radar” (previously released on Blackout) is a puzzler–it’s a good track, but it’s not included-on-two-consecutive-albums good. […]