Damning with faint praise? Poppea is ... interesting.

The last outing of this year's country house opera season was all about experimentation. New accommodation, new opera, new pitch for the marquee. The last was probably the most successful.

After more than two months of dry, hot, still weather, a thunderous cold front driving torrents of rain came ripping through England on the night we were due to be dining al fresco on the Longborough Opera Festival's lawns. Fortunately we'd brought our marquee, though the space we've erected it on for years has been taken over by the patrons' dining tent. Not having reserved a spot within, we set up in the patron's parking area, where we discovered that the marquee fits precisely within a small grove of trees and that lashing two of its legs to their trunks kept the whole thing from going airborne in the worst of the gusts. The new location lacks the expansive views over the valley you get from the top of the meadow, but was just 20 metres from the entrance to our box. Add four gorgeous courses meandered through before, at the interval of, and after the opera, and you have the delight of the evening.

The Coronation of Poppea was more interesting than enthralling. Monteverdi's tale of the rise of Nero's second empress is still in the modern repertoire for two main reasons: it was one of the first operas as we know it, so an important ancestor of all to come, and it closes with one of the most beautiful love duets in classical music. (Second only, I believe, to Mozart's La ci darem la mano.)

Pur ti Mio, Pur ti Godo (I gaze at you, I possess you) perfectly captures the passionate ache and ecstasy of a relationship in its early glory, and is almost worth sitting through the 2.5 hours before it just to hear it live. That's not to say the preceding opera was bad, it's just very much of its time. There's a lot of ponderous harpsichord, undeveloped characters and vocal fireworks in search of a more memorable tune. I suspect that had it been performed as written ... essentially a court masque with outrageously lavish sets, costumes and special effects ... those irritations would have been less noticeable. But nobody does traditional anymore, and Longborough's small stage and tight budget couldn't finance a Baroque treatment even if they wanted it.

Instead we got a strange mix of Roman, Viking and modern "Street" costume with brutalist pillars and a few curtains as the only stage setting. The gods wore high tops, backpacks and neon-illuminated hoodies, and punctuated the action by scrawling graffiti on the central wall. When they scrawled GRIME, and then later preceded it with LA, was I supposed to read the Italian word for tears or as a fashion commentary that helped me understand the characters? The programme added little, asking us to consider not the historic Nero but a metaphorical one who lives in a "cubist, splintered hall of mirrors, that allows us to explore the perilous brevity of time and instability of place and history." Don't let years of brilliant reviews go to your head, Longborough. You're in danger of disappearing up your own backside here.

This was the young performer's production, which Longborough always uses to go experimental on staging. Often, it works. (Rinaldo set in an early 20th-century carnival was a triumph.) This one didn't. My bigger problem, however, is with the opera overall. Monteverdi is playing with morality, turning some of history's most awful people into heroes. It's hard to get excited about the main characters when you know that Nero divorced, exiled and starved to death his first wife, Ottavia ... sung here with stoic dignity by Maria Ostroukhova... then presented her head in a box to the gleeful Poppea. Or to take that final duet seriously when you know that an unhinged Nero kicked his pregnant new wife to death six months later. (And then forcibly castrated a slave boy who looked like Poppea and had him pretend to be the dead woman, returned to life. Seriously, this guy was bad news.)

 The voices and music, however, lived up to Longborough's usual standard. Anna Harvey's Nero, Sofia Troncoso's Poppea and Matthew Buswell's Seneca all gave particularly strong performances. There's a pleasing sub-plot between Ottone (Matthew Paine) and Drusilla (Lucy Knight) that's the most dramatically engaging part of the opera. Jeremy Silver's orchestra, with a full complement of period instruments and him conducting from the harpsichord, brought our ears the Baroque lusciousness that our eyes were denied.

We'd seen Harvey as Bradamante in Longborough's 2016 Alcina, and Knight as one of the spirits in The Magic Flute last year. It's great to see familiar faces progressing into bigger roles. And equally exciting to see all the Longborough debuts. Crazy staging aside, there's no question this is becoming one of the foundries for operatic talent in Europe.

The whole production team deserves special praise for coping with an opening night disaster: the storm that didn't take our marquee did blow out the sound board, forcing an early dinner break and putting the whole production an hour behind schedule. The show continued to that magnificent concluding duet without throwing anyone off their stride.

And there, at last, came a bit where the strange setting worked. As Poppea's and Nero's voices entwine in the majesty of love, the gods link words together on the graffiti board to say "Words mean nothing anymore". In light of the karmic justice awaiting the couple (Nero only makes it three years after murdering Poppea before he's forced to suicide), it's a profound, ironic and hugely depressing way to end the story.

I'm thankful to Monteverdi for helping to create one of my favourite entertainments, and was intrigued by this exploration of operatic roots, but I admit to breathing a sigh of relief that his cynical celebration of anit-heroes didn't become a staple of the art form.