What The Night Is For, Comedy, London <br></br>Dinner, NT Loft, London <br></br>Coriolanus, Swan, Stratford-Upon-Avon

X-rated? Nope. So what else is on offer?

Adam Penzius pours himself another flute of champagne. Then he softly tops up Melinda Metz's glass while she fields a phone call from her suspicious husband. What The Night Is For, by Michael Weller, starts off with Roger Allam's Adam and Gillian Anderson's Melinda merely having dinner, both fully dressed in business suits. But this obviously isn't all that's pencilled into their diaries. Workaday ties, of one sort or another, will soon be loosened. In fact, this new seriocomic US romance – in which the star of The X-Files is making her West End debut – is set in Melinda's hotel room. And it's going to get a tad steamier than the comparable private supper, with room service, in Noël Coward's Song At Twilight. If you need a more sizeable hint about what's to come, the huge crimson double bed, upstage in John Caird's production, may give you a clue.

We rapidly gather that our duo are old flames who met at a book club and had an extra-marital fling a decade ago, before Melinda suddenly quit New York leaving no message. Having traced her, Adam is clearly keen to rekindle their affair. She appears, by comparison, somewhat frosty and evasive.

Nevertheless, given time she thaws, they inevitably head for the bed, and their tête-à-tête becomes an increasingly frank confession of their obsessive love for each other. Melinda's years of suppressed grief and mental instability are exposed as well.

Fundamentally, the questions hanging over this pair are as follows. How mutually committed will they be beyond tonight? Is following their impulses the right course of action? And can their marital and parental commitments fit with their fantasy of getting back together? Anderson proves herself a fine stage actress. Her Melinda is a rather intriguing mix of barbed small talk and nerves – staring hard at her plate as Allam leans towards her. Flashes of girlish, teasing humour then start bursting through, and later she grows alarmingly frantic. Allam, though, is more riveting and touching with his mix of slouchy relaxation and ardour. Perhaps he underplays his character's darker, selfish side, but his seductive moves are full of warmth and yearning. In terms of sexual chemistry – or physics – he seems drawn to her body as to a lodestone, stretching out his fingers hesitantly to touch her hips.

Weller's two-hander doesn't really merit such a grand world premiere. It can be very entertaining, depicting awkward erotic moments and circumlocutions. Anderson memorably cocks an eyebrow at Allam's euphemistic suggestion that, "Maybe we could say 'hallo' from time to time." Some suspense is generated too as Melinda's spouse is probably on his way and could catch her in flagrante or, at least, in the company of a telltale hostess trolley bearing dirty crockery for two.

Regrettably, the plot developments can seem slow moving and Tim Hatley's vast set works against a sense of intimacy. Caird's policy of non-nudity seems coy too, not to say coitally challenging, though maybe pyjamas are understandable after all the leering over Nicole Kidman in The Blue Room.

Beyond that, Weller's sprinkling of literary references is very superficial. You never believe for one minute that Melinda was formerly a brilliant young Manhattan poet. And the dialogue does have a nasty habit of turning corny at times. Melinda's cries of "Moo!" – alluding to a weak-kneed toy cow she's given Adam as a present – caused my toes to curl.

Dubious ethics and marital bitterness mean the prandial conversation is less than civilised in Dinner at the National's Loft space. Moira Buffini's new social satire is a neo-gothic evening. Greeting her sinister butler with a kinky kiss and a fat brown envelope, Harriet Walter's Paige is a hostess from hell. A witchy femme fatale in a scarlet sheath-dress, she crushes her guests and unfaithful husband, Lars (smarmy Nicholas Farrell) with poisonous snipes and gastronomical horrors. The butler serves up frozen garbage for their deserts. Retributive justice is manifestly a central theme and amoral egocentricity is a topic for debate as this supper is meant to celebrate Lars's best-selling philosophy book, entitled Beyond Belief.

Buffini enjoys sending up Lars's media-hyped rot about "freeing oneself from liability" to pursue aspirational fantasies as "the god of your own psyche-drive." Often, Walter's gruesome eloquence is splendidly arch too, declaring of her algae soup that, "the great thing about this dish is the leftovers breed." Penny Downie, as the touchy-feely vegetarian Wynne, looks distinctly green by this point. Class aggro is added when Paul Rattray's Mike, a van driver, rings on the bell and gets sucked into the mire.

Walter is on excellent form. She's icily witty and becomes drunkenly desperate near the end. Indeed Fiona Buffini (Moira's sister) directs a strong ensemble with aplomb and Rachel Blues' chic, funereal set is potently claustrophobic. The trouble is that most of the dramatis personae remain two-dimensional, the gothic dinner scenario feels dated. Some plot twists – including the savage finale – are strained, and many speeches are so stylised they feel lifeless.

Coriolanus all too often comes across as a cold, dreary saga about an emotionally constipated, crushing snob in a toga. What's thrilling about David Farr's staging – the most gripping RSC production I've seen in a long while – is that political conflict seems intensely personal and immediate.

You might not expect that, given that Farr and his designer Ti Green have taken Shakespeare's tragic hero – who's expelled from Rome for pleb-scorning pride – and turned him into an ancient Samurai warrior. Yet Farr deftly combines Eastern and Western cultures. Beautiful, simple silk kimonos and haunting Oriental music – featuring quivering flutes and rapid drumming – are smoothly woven in with essentially very British, psychologically clear, naturalistic acting. There are also tongue-in-cheek modern touches with Richard Cordery's winningly wry Menenius sporting a cloth cap, and as the tribunes, Tom Mannion and Simon Coates have the Brylcreemed hair of slippery MPs.

Though Greg Hicks can be a highly mannered actor, here he keeps the ritualistic to a minimum. His wiry, craggy-faced Coriolanus has a hooded expression that only flickers with emotion. Yet you discern a marked humorous streak that makes him startlingly sympathetic, countering his diplomatically hopeless, flaring arrogance. His fierce sense of his own worth is also perceptibly combined with flinches of anxiety when surrounded by the masses. Hannah Young is, unfortunately, just too ridiculous as his weedily shrieking wife, but everyone else pulls their weight and Alison Fiske is firing on all cylinders as his possessive, aristocratically growling mother. Not to be missed.

k.bassett@independent.co.uk

'What The Night Is For': Comedy, London SW1 (020 7369 1731), booking to 23 Feb; 'Dinner': NT Loft, London SE1 (0207 7452 3000), to 14 Dec; 'Coriolanus': Swan, Stratford-Upon-Avon (01789 403403), to 25 Jan