Before anything, I must apologize to Led Zeppelin fans; I can't
give you any word on whether arranger Jaz Coleman managed to
capture the spirit of Led Zeppelin's music in his score. I haven't
had the opportunity to listen to any Led Zeppelin whatsoever;
whenever I ask my friends about them they lend me Pink Floyd's
Dark Side Of The Moon.
The approach is unusual for rock music arrangements. Symphony orchestra is different from Hollywood-type pops orchestras or brasswind orchestras; the emphasis is on strings, the brass sounds muted and the whole feel is wide open, "out there." While it's easier to avoid melodrama, it's harder to make an impact.
And some songs need the impact. "Kashmir" drags heavily on strings and the guest instruments sound cheezy in their attempts to sound oriental. "Stairway To Heaven" starts out beautifully but fails to go all the way, not even in the epiphany section with the brass being muted (typical symphony style; I played trumpet in one but quit after a year because the brass never did anything interesting).
There's also problems with score. Symphonies tend to ramble but "Going To California" and "Friends" are almost nonsensical. "All My Love" has beautiful string scoring but the mood is ruined by an out-of-place trumpet theme. It works in "The Battle Of Evermore" but that's largely due to the uilleann pipe (a non-symphonic instrument) solo played by Liam O'Flynn, on which the arrangement is build around.
The arrangement of "When the Levee Breaks" is fantastic, however; its complexity is tackled willingly by the musicians with gut not frequently seen in symphony orchestras. Along with "The Battle of Evermore" and the beginning of "All My Love", it makes up the high point of the entire album.
On one hand, it was probably a good idea to use a symphony orchestra; anything louder would've competed with the original versions. But it should've gone all the way. Any use of synthesizer or special effects were obvious and distracting; a straight symphony album would've done better, gone deeper. Led Zeppelin fans would have to judge for themselves but try to be sympathetic to the arranger; he's a Led Zeppelin fan, unlike pedestrian me.