The RSC's first production of Troilus and Cressida for six years finds us renewing our acquaintance with the Greek camp, the Trojan camp and plenty of other varieties of camp. An early casualty, in this playful context, where the grim realities of war take second place to preening and posturing, is the scabrous commentator on events, Thersites.

Richard McCabe bounds on - straggly blond hair, bug-eyes - to deliver the prologue with the fruity histrionics of John Sessions. This turns out paradoxically to be a fairly monotonous thing to do. In Ian Judge's production, McCabe finds himself surrounded by attention-grabbers. Just look around. The Greek warrior Ajax (Ross O'Hennessy) has the physique and skimpy costume of a Chippendale and speaks with a lugubrious Welsh accent. Cressida's uncle, Pandarus (Clive Francis), has a pasty face, a mincing walk, and the suggestive intonations of a Trojan Kenneth Williams. He tugs, winsomely, at his black ringlets and barely controls his excitement when Hector (Louis Hilyer) passes. The taciturn Patroclus (Jeremy Sheffield) mysteriously shuts Thersites up with a big kiss. And so on. It's down to Philip Voss, as an impressively articulate Ulysses, to anchor the play's political and social concerns: mellifluous and acidic, with a basilisk smile, when Voss speaks we hear each syllable. Elsewhere, sexuality is everywhere and nowhere, spreading a tired theatrical gloss on passion and eroticism.

The sexual chemistry between the young lovers - played by two of the RSC's brightest stars - never materialises. The excellent Victoria Hamilton, who is in the fast track of British theatre (she recently shone alongside Alan Bates in The Master Builder), makes a flirty, quick-witted Cressida. Give her some red specs and she could present a late-night arts programme. She's down-to-earth, modern and precise. Even when she is indecisive - as she is when alone in the Greek camp with Diomedes (Richard Dillane) - she is decisively indecisive.

The sensitive, romantic Joseph Fiennes (younger brother of Ralph) looks perfect for sensitive, romantic Troilus. He keeps himself in a state of perpetual emotion. He wobbles his head. His voice quavers and warbles, rising delicately at line endings. This is before anything much has happened. When something does happen (Cressida leaving, say) his voice has nowhere to go. When Fiennes explodes at Diomedes ("Grecian, thou dost not use me courteously..."), I heard the voice of another fretful loser: Frank Spencer in Some Mothers Do 'Ave 'Em.

Judge handles the battle scenes well: the ritualised warfare is choreographed by Lindsay Dolan. John Gunter's designs of the battered walls of Troy - with fiery sunsets that glow across the backdrop - move us quickly between rival armies. But within the rival camps of this production, the wrong one triumphs.

In half a dozen plays written specifically for the RSC, the American playwright Richard Nelson has explored Anglo-American relations. In his latest, The General from America, he focuses on Benedict Arnold, the American general who in 1779 attempted to hand George Washington over to the British. Arnold sounds the Brits out while the suspicious Americans sound Arnold out. Will he be rumbled? It has the makings of a defector thriller: an 18th-century version of the Sean Connery movie The Hunt for Red October.

Nelson is too suave a dramatist for this kind of crowd-pleaser. With an elegant touch he debunks his material. This works excellently when depicting the shifting, provisional atmosphere in which America found its independence. What it means to be American is caught at an embryonic stage. Chance and mishap rule. When Arnold (James Laurenson) meets with British intermediary Major Andre in a field near the Hudson, Andre, played quite broadly by Adam Godley, gets laughs as the foppish beanpole poet and actor who won't stop drinking. This deflates the drama. The plot hinges - perhaps truthfully, certainly flimsily - on Arnold's wife stopping Arnold's sister from giving her a crucial piece of news because she wants to go to bed. Nelson has developed his own genre: the ironical history play. The General from America lacks the big scene that crystallises all the others. Like Arnold, for all its promise, it fails to deliver.

Laurenson never gets a chance to impress us as the general. He's always on the defensive: blustering, evasive, offended. Nelson doesn't takes us far enough inside his mind to involve us in a crisis of conscience. Laurenson looks happiest in his dealings with Corin Redgrave, the chuckling, watery-eyed, jowly George Washington, who mocks the fact that the British have offered to name a city after him if he surrenders.

In Howard Davies's production, atmosphere is largely provided by Martin Slavin's soundtrack. There are good performances from Jay McInnes, as Laurenson's young wife, shooting sharp devotional looks to her husband; Stephen Boxer as the chilly Major Kemble; and the alert, intelligent David Tennant as Hamilton, Washington's secretary, who firmly interrogates Arnold while holding a quill in one hand and a cup of tea and a piece of cake in the other.

There's a moment in The Lights, a new play about city life by Howard Korder, first premiered in New York, when the two shop assistant girls have been picked up by two blokes, and gone back to one of the blokes' apartments, and suddenly something starts to happen. Well, a play starts to happen. The Lights ceases to be about dislocated lives, the millions who live one on top of another, the odyssey from innocence to experience, and becomes a scene about four people in an apartment who only met that evening. It doesn't last. The Lights is one of those plays (set, naturally, in an unnamed city) where it doesn't matter where characters are - shop, bar, hotel lobby, skyscraper, abandoned building - they invariably discuss an aspect of the play's theme: city life.

Ian Rickson's Royal Court production places the audience on the stage and the actors on the three levels of the auditorium. It gives us the split levels, but blurs the focus. Deirdre Harrison powers the show as the feisty Rose, leading her emotionally inchoate friend Lilian (a wispy, angular Emily Mortimer) in and out of trouble. Lee Ross quickly palls as the anguished jilted boyfriend, and Colin Stinton turns in a colourful cameo as the champagne crook who leads the girls back to his apartment. If only we stayed there.

Theatre details: Going Out, page 14