Let's get the one clear negative point out of the way first: this is a short measure at only about forty eight minutes. I'd agree with the reviewer who decided to knock a star off for that.
Now to the more positive aspects; very fine playing well recorded and a very intriguing work. There are good reasons why this symphony could fail but it is a very effective work. Firstly; Rihm is happy to talk at length about the formal processes behind building the work and to suggest that it takes indirect reference to Brahms and builds a formal path that perhaps Brahms might have taken today. That is, frankly, empty naval gazing and the references to Brahms seem pretty direct to me even if they don't quite amount to direct quotation.
Each of the movements takes references from one of Brahms' symphonies with the second movement a song that references the creating process. Again, the song movement is pointless naval gazing but it helps break up the consciously Brahmsian orchestral palette of the other movements.
The whole doesn't sound so much a contemporary update of Brahms but sounds very familiar all the same. His chromatic musical language echoes early Schoenberg - his chamber symphonies, in particular. Another similarity, maybe a surprising one, is with Charles Ives. Ives' was taught, and influenced, against his will perhaps, by a Brahms disciple. His orchestration, therefore, carries the same palette and similar counterpoint when he was behaving himself. The slower sections are harmonically similar to his Third Symphony and the slow introductions in his "Holidays Symphony". That work is essentially a suite of tone poems and Rihm's symphony feels closer to that than a robustly argued Brahms symphony.
I could talk at length about Rihm's referencing of post -modernist models in his style but the important thing is that this symphony works so well. Brahms' voice echoes through each of the movements but their journey seems far freer with each presenting a varied journey from beginning to end. His referencing of Brahms is far more subtle than the polystylism of Alfred Schnittke but, like him, there's a sense of fantasy, rather than romantic symphonic rhetoric, about the journeys he takes.
Like much of Wolfgang Rihm's best music this symphony is never short of beguiling.