One could spend an awfully long time searching for two more contrasting productions. Verdi's final opera, Falstaff, is frivolous, fun and musically dense: the Scottish composer Judith Weir's 1987 opera, A Night at the Chinese Opera is measured, demanding and often extremely sparse. With a list of contrasts longer than the Great Wall, these operas do not really fit together. But that appears to be entirely the point. What Scottish Opera achieve here is a reminder that despite fundamental differences between contemporary opera and that of the nineteenth century, despite the strangeness and complexity of Weir's work, standards of humour and of beauty are, for the most part, timeless.

The company's Falstaff undoubtedly comes an an odd time, following almost immediately on from Welsh National Opera's production starring Bryn Terfel in the title role. Enough glowing words have been written about Terfel, one would think, to unsettle followers on this year. In fact, Peter Sidhom is a fantastic Falstaff, showing no signs of an attempt to fill Terfel's fat-suit. An amalgam of The Merry Wives of Windsor and the Henry Plays, Falstaff tracks the famously fat knight's attempts to woo both Meg Page and Alice Ford at the same time. Convinced of his own powers of seduction, Falstaff is lured into several humiliations, including a dunk in the river which he survives only as a result of the buoyant properties of his belly. But in Sidhom's hands, the knight is not just "enormous Falstaff": Sidholm's Falstaff, of course, is ridiculous and brash. His voice rises, rich and satisfying, from deep in his belly. But he can also be paternal, magisterial and, at times, menacing. When he sings in typically aggrandising fashion of himself and points, hilariously and unwittingly, at a large wine stain on his grubby vest, there's a guilt in the laughter which is ever so slightly moving. It might be hard to laugh at Sir John were he not so damn funny.

He is supported by a here by a strong cast. Falstaff is lauded for the way in which Verdi and his librettist Arrigo Boito fused music and text and, under Peter Robinson's baton, this is the source of a great deal of fun. The cast are constantly engaged in slick synchronisation between music and action, erring very much on the side of slapstick. In another opera, the business might seem too much. But, since it lacks an overture, Falstaff must hit the ground running. This is achieved not only through careful choreography and an orchestra more than nimble enough to shadow it, but also through clever stage-setting. The first scene in the Garter Inn, for instance, distorts the perspective of the set with an angled beam across the proscenium arch. It's a subtle touch, but one which provides an exciting, disorientating stage picture for the opening drinking scene. Plaudits here must also go the female cast members who collectively comprise the Merry Wives of Windsor. Their scheming together could risk feeling like a necessary prelude to the hilarious denouements with Falstaff. Here, however, the women's energetic vocal acting—laughing, goading and mock impersonating—gives a real edge, as well as a lovely sense of cameradie to their ensemble work. The opera's real love interest, Nannetta (Lucy Crowe), in particular hits just the right balance between bold feistiness and a captivating romantic lyricism.

There is, however, one sour note struck, frustratingly, in the final scene. It's a shame, since Dominic Hill's staging of the episode, in isolation, is interesting. Set in Windsor Forest, the scene sees Falstaff tormented by evil sprites and spirits – in fact another trick arranged by the viciously merry wives. To denote the forest and, perhaps, to spirit in a touch of magic to accompany the other-wordly pageant, Hill has tree trunks drop from the rafters, ripping through paper panels in the set the remaining suspended in mid-air. Undoubtedly, this is visually appealing, and the idea of ripping the set prods at ideas about the artificiality of opera and of its ludicrous goings-on.

The problem is that this sits ill at ease with the rest of the production, which stays firmly on the side of the real, rather than the surreal. This is a production which delights in the ludicrous goings-on, lavishing not only believability, but also pathos upon Falstaff's trials. It is a production in which Falstaff is credibly dirty and balding, rather than wholly ridiculous, meaning the humour springs from fully formed—and grossly flawed—characters, rather than types. It is a production which works by allowing Verdi's music to poke fun at the action, leaving the characters for the most part unaware that their reality is an elaborate ruse. The final fuge, 'Tutto nel mondo è burla' ('All in the world is a joke'), could be a real revelation. Instead the trees pre-empt this and, as such, seem more appropriate to a very different production.

This sense of the uneasy trickery of opera, is much more of a focus point in Judith Weir's A Night at the Chinese Opera. Premiered in 1987, the piece has been seldom performed since. It's not tough to guess why: A Night at the Chinese Opera is hard work indeed for an audience in a way that Falstaff is perhaps not. And yet, despite the contrasts, the decision to place these works alongside each other at the end of the season appears to be very well judged. Falstaff is a reminder that Verdi, the great tragedian, was also an excellent comedian. Here it is also serves as a reminder that opera may well achieve nothing if it fails to entertain. In recognising that there lies a great deal of fun in Weir's complex opera, Lee Blakeley makes this point with aplomb.

It's a clever decision since, without making such links, one risks stranding an audience with very little to compare A Night at the Chinese Opera to. Overlapping layers of plot and of music unravel the story of Chao Lin who, orphaned after the invasion by the armies of Khubilai Khan, is driven by a misconception of his own fate towards tragically failed rebellion against his masters – masters under whom he has had great success building roads.

Cast adrift from familiar musical languages of mood and of character, Damian Thantray does brilliantly to flesh out the character of Chao Lin. Weir's music is exceptionally sparse and the doubling of instruments with vocal lines leaves little space for the sort of vocal inventiveness seen in Falstaff. But far from proving an obstacle, this produces beautifully taught passages of music and a tension between vocalist and orchestra in which subtle changes in instrumentation or vocal styles precipitate thrilling swings of mood or emotion. The director helps here, having cast a very striking looking actor in Thantray, whose strong facial features flicker between the imperious road-builder and the vulnerable orphan.

Elsewhere, however, looks prove less successful: the Military Governor, a counter-tenor, is frankly ridiculous with his shaven head, thin moustache and all in one robe. Sartorially correct, perhaps, for a figure-of-fun despot, the Military Governer is anything but. Reno Troilus is, in fact, vocally superb in the role, avoiding the man-with-squeaky-voice pitfalls which can make a counter-tenor seem effeminate. Instead, Troilus is cold and precise: in the final act when the tyrant's robe is unbuttoned to reveal glimpses of skin, the physical, latently violent edge here is far more chilling than a twee moustache could ever achieve.

His counterpart, Nicholas Warden as the Mongolian soldier, is truly menacing throughout the performance, particularly in the scene which sees the Military Governor and the soldier singing together, Warden's very deep bass and Troilus's high, aloof counter-tenor jarring at the extreme ends of the male vocal spectrum. The effect is startling: the physical and intellectual levels of military dictatorship clash and pull away from each other, but unite at that moment to squeeze out all of the voices onstage. Weir writes here of the terrifying coerciveness of rule by force, and Blakeley's production seizes upon opera's uncanny ability to reproduce this terror.

However, Warden skulks around the set maybe a little to much. It's a very slight criticism, but where most of the movement elsewhere is so beautifully choreographed this stands out, particularly in comparison to the triad of actors who tackle the play-within-a-play – 'The Orphan of the Chao Family'. Precise, varied and highly stylised, much of work's comedy and visual appeal—of which there is a great deal—stems from here. The shadow-puppet work behind (and in front) of an illuminated screen, one suspects, is the central set piece which can really make or break this opera since its themes and images extend throughout the work. It is a long scene and, here, the energy levels and excitement never dip. The vocal dexterity of the three is terrific, each negotiating multiple accents and styles with great success. Maze-like and beguiling, A Night at the Chinese Opera is a truly intriguing piece of contemporary opera.