It's turned into an Oxford Greek festival. First came storytellers Hugh Lupton and Daniel Morden presenting a Greek cycle. Soon Shared Experience visits the Playhouse with its free adaptation of Euripides's Orestes. And this week Welsh National Opera stages its new production of Monteverdi's The Return of Ulysses at the New Theatre.

Ulysses presents a director with quite a challenge. The plot can be summarised in seven lines of type, yet, in this production, Monteverdi's opera runs for the best part of three hours, excluding an extended interval. There are also lengthy periods of recitative, when not much action occurs, either on stage or in the orchestra pit.

Director David Alden goes for two solutions to the problem. First, he produces an inventive, bright, and brittle stage spectacle, which he uses to incorporate black, and at times almost manic, humour. Second, he, and specialist Monteverdi conductor Rinaldo Alessandrini, extract as much individual characterisation as they can from the voices of their singers.

The staging works best in the second half, when we are introduced to all manner of seedy suitors and hangers-on to Penelope's household. There is a telling scene when various huffing and puffing suitors vainly attempt to stretch the string across Ulysses's bow - Ulysses is Penelope's currently absent husband. And there is an even more telling moment when giant eagles - or are they vultures? - swoop down on the decadent goings-on, which have been orchestrated by Eurymachus (Andrew Tortise, giving an excellent impression of a lower-level Mafia lieutenant). And as light relief, there is the glutton Irus (robustly sung by Neil Jenkins), who appears to run a mobile pizza stall: "Instead of succumbing to hunger, I would rather my body fed the grave," he assures us. Penelope, however, remains faithful to Ulysses.

But unknown to them all, Ulysses has now returned. He is dressed as a beggar, and sits in a wheelchair, hunched and ignored. "If your highnesses will permit me, I'll trample your filthy bodies under my feet," he remarks with biting sarcasm. But nobody hears him. Paul Nilon gives a magnificent performance in the title role: vocally incisive, with every inflection and piece of ornamentation in place, he is equally riveting as he sits, silent and motionless, in his wheelchair.

Meanwhile Sara Fulgoni, as Penelope, is a little less attuned to Monteverdi's vocal line, but is nonetheless moving, particularly in moments of dark despair. Elsewhere, Alden doesn't always manage to involve you with the rather cardboard and confusing minor characters, and the singing is a bit variable. But there are splendid contributions from Sarah Tynan as Penelope's highly available maid Melantho, and from Elizabeth Vaughan as Ulysses's old nurse. In the pit, conductor Alessandrini keeps tight control of the timing, and extracts some thrilling flourishes from the WNO string players.