At the premium price that LSO Live are asking for Gergiev's Mahler cycle (sans ANY song cycles, Das Lied von der Erde, Das Klagende Lied or finished 10th), there are better choices that one could make. To look on the positive side, it is nice to have a 'Russian' take on Mahler, captured in more modern sound - "Russian" meaning that tempos are on consistently on the fast side, as though Mahler were little more than a precursor to Shostakovich (or an after-thought to Tchaikovsky). Needless to say, the London Symphony play quite well throughout the cycle.
But a big stumbling block is the generally 'dry' and 'boxy' acoustic of London's Barbican Center. To my ears, the best item in the cycle is Gergiev's surprisingly solid Mahler 8th from London's humongous St. Paul's Cathedral. The 8th featured a lineup of mostly young Slavic singers, and they do a really good job. On top of that, the recently refurbished organ in St. Paul's makes a sizable contribution. It's also nice to hear several seconds of sound sloshing around in the dome after each part (it's a two-part symphony). Also, Gergiev's cycle got off to a nice start with a fast and furious performance of Mahler's 'tragic' 6th symphony. But beyond that, I just don't hear much that truly distinguishes Gergiev's Mahler.
His 7th has an exciting and raucous finale, but the rest of it isn't terribly special. The 3rd is a pretty fast 'run-through' from start to finish, which isn't necessarily a bad thing with such a lengthy and diverse symphony. The "Resurrection" (#2) was quite exciting also, but the scherzo was just absurdly fast - almost like a needle skating across the surface of vinyl, missing the grooves altogether. Yes, I'm exaggerating but it's to illustrate a point. The 'other worldly' feel to the last movement of Mahler's 9th is completely missed at such a quick tempo. The 4th was just plain 'weird' in places.
So yes, you could do worse but you could also do better. Bertini, Chailly and Bernstein (Sony or DG) are far more attractive options (with a LOT more bells and whistles included). Even Simon Rattle - 'weird' and eccentric as his Mahler can sometimes be - gives more insight into the core of Mahler. Keep in mind that complete cycles are well on their way from both Markus Stenz (Cologne) and Manfred Honeck (Pittsburgh) - both interesting and fully idiomatic 'interpreters' of Mahler in their own right. Even though I don't care for Tilson-Thomas' conducting in his San Francisco cycle, the sound quality is significantly better than what we get from London's Barbican (if also a bit 'glitzy' sounding from S.F.'s Davies Hall). The best deal of all is EMI's 16 cd, "Mahler - The Complete Works" box.