As a standalone piece of symphonic music I found Colin Matthews' enlargement of the Piano Quartet movement good, however it doesn't quite sound like how Mahler would have orchestrated it. It doesn't sound much like Mahler, but rather Tchaikovsky. The way the cymbals are utilized in the climaxes sounds like the Romeo and Juliet overture, and the usage of the bass drum reminds me of Manfred, to be specific. It's hard to say because to me Mahler's piano quartet sounds vastly different from everything else he composed.
When the tam-tam entered at the end I was like "ahh, there's Mahler!" Like I said though, solely as a piece of symphonic music it's enjoyable.