The Effect National Theatre: Cottesloe, London
In Lucy Prebble's provocative and darkly equivocal follow-up to Enron, a clinical trial for a new drug throws up profound questions about what brain-chemistry can – and cannot – tell us about falling in love and the causes of severe depression. Also acute about the vested interests in the debate.
The River, Theatre Upstairs, Royal Court, London
No director has a finer grasp of the musical structure of a play than Ian Rickson. This was demonstrated again in his exquisitely modulated production of Jez Butterworth's haunting new drama (a chamber piece after the full orchestra of Jerusalem) about memory, desire – and fishing.
Richard III/Twelfth Night, Shakespeare's Globe, transferring to Apollo, London
The protean genius of Mark Rylance is at full throttle in his astonishing double-bill as a Richard III whose psychotic impulses slip out from behind a mask of buffoonery, and a hilariously fluttery Olivia, gliding around like a geisha on casters as she struggles to contain her passion.
Merrily We Roll Along, Menier Chocolate Factory, London
Maria Friedman made an amazing directorial debut with this thrillingly assured and perfectly cast revival of the notoriously tricky, richly rewarding Sondheim musical. The show takes a trio of friends on a backwards journey from the compromises of middle age to youthful idealism.
Going Dark, Young Vic, London
An astronomer who is gradually losing his sight talks to his little boy and delivers lectures on a universe that is itself going dark in this wondrous piece. It's presented as an immersive experience in various degrees of blackness and with an eloquent text by Hattie Naylor.
Discovery of the year: Mhlekazi “Whawha” Mosiea
Effortless stage magnetism; the mercurial ability to spin on a dime from tragic to comic; a gloriously supple tenor voice – you can check out the phenomenal gifts of this black South African newcomer when the Isango Ensemble return to the Globe in 2013 with Venus and Adonis.
Turkey of the Year: King John, Swan Theatre, Stratford-upon-Avon
The RSC's abysmal production of King John subjected this unfamiliar, politically acute history play by Shakespeare to the kind of trite, tonally messy and nervously jokey updating that stinks of insufficient faith in either the text or the audience's intelligence.