Last night's viewing - Freddie Mercury: the Great Pretender – an Imagine Special, BBC1; Order and Disorder with Jim Al-Khalili BBC4

There is no disputing Freddie Mercury's greatness, or the charisma of his performances and how far the on-stage flamboyances diverged from the shy, RP-accented man he was out of the fan-filled stadiums. What is at contention here is whether we needed another Freddie Mercury documentary, so soon after BBC2's Queen documentary last year.

For some of us, it doesn't seem all that long ago that his death was announced, in November 1991, 24 hours after Mercury confirmed that he had Aids, upon which followed various TV homages that reflected on the dualities in his life, his so-called "secret" homosexuality, his HIV and of course his supreme talent for music. Alan Yentob's Imagine series promised to take us in a different direction with Freddie Mercury: the Great Pretender, though even the title seemed a touch tired. This would, apparently, show us the real man, and one who was itching to forge a solo career. We'd see new and rarely seen footage. We would, in all of this, presumably learn something new. Did we? We may have done but, overall, it felt rather more like a trip down rock memory lane than an hour of revelation or revisionism.

This isn't to say that Mercury's presence wasn't absorbing. He was an enthralling performer. Here he was again in all his pavonine glory, a camped-up, balletic "macho man", singing " I Want to Break Free" wearing fake breasts. He was a rock star who was able to mesmerise his audience with his big, thrilling presence as confidently as a magician casting a spell. It was also touching to be reminded of his off-stage vulnerability, in the one-to-one interviews in which he spoke about life and – heartbreakingly – about love ("The more I open up, the more I get hurt").

But the déjà vu in it all was so pronounced that it felt more like a repeat than a new documentary. One over-familiar "talking head", Paul Gambaccini, didn't exactly help, having just drawn breath from his reflections on The Beatles in a BBC documentary last week.

We were taken on a brief tour of Mercury's early years, which were got through a little too routinely (cue piano music for childhood photographs and brief musings on how his itinerant family life in Zanzibar and India left him unsettled). Then we trod more familiar ground over his special relationship with an early girlfriend, Mary Austin. Brian May and Roger Taylor were there, talking about their incredulity at his terminal diagnosis and his musical virtuosity. Thankfully, there was some unexpected material – Mercury recorded with Michael Jackson and liked to bring his pet lama into the studio, and an interview with Spanish opera singer and collaborator Montserrat Caballé revealed that he stopped kissing her on the cheek when he found out he was HIV-positive. These were surprising moments, but not enough to sustain the freshness of the hour.

Jim Al-Khalili took us through the rules of thermo-dynamics in Order and Disorder, with accompanying images that were so big and vivid that, at times, they resembled the wacky, molten-earth bits from The Tree of Life. Aside from these interludes – as bizarre here as they were in Terrence Malick's film – this was a stimulating hour that made science sound very close to metaphysics. The upshot of it all was that all energy was destined to degrade and atrophy. In layman's terms, it sounded like a theory of mortality, on a universal scale. There is a finite amount of energy in the universe, and while humans have learned to harness its "flow", our challenge now is to unlock more concentrated forms through hydrogen atoms. There is where Al-Khalili lost me, but it didn't seem to matter. Great rousing statements kept me afloat, such as, "The universe shares the same fate as a cup of tea", and "science is all about seeing what everyone else has seen but thinking what no one else has thought."