I had high hopes for Julian Anderson’s first opera, Thebans. Premièred at the Coliseum last Saturday, it promised to mark a departure from the trendiness of ENO’s recent commissions, Nico Muhly’s Two Boys, for example, or the dreadful Sunken Garden — in fact, ENO’s next season seems to reflect a company at last a little less enamoured of innovation for its own sake.