FESTIVALS ARE notorious for generating a certain amount of hyperbole among frenetic, sleep-deprived critics who - having waded through a swamp of mediocrity - are prepared to declare that the next competent spoon player is, in fact, a genius. However, this National Theatre of Scotland revival of Anthony Neilson's 2004 Edinburgh Festival hit The Wonderful World Of Dissocia proves that the play is, if anything, even better than the enraptured reviews gave it credit for.

Tackling the complex issue of mental illness and our society's approach to it, the drama exhibits real bravery in the boldness and sensitivity with which it explores the psychosis of Lisa, the young woman at the centre of the play. As Lisa is pulled into the alternately beautiful and appalling vortex of a psychotic episode, Neilson unfolds before us an extraordinary imagined world, full of hilarious, yet disconcerting, characters (whose very names - such as the desperately self-critical "insecurity guards" - sound like the result of a word association game played while on hallucinogenic drugs).

Dissocia is a sort of Alice In Wonderland for the 21st century, taking us into a looking glass world in which the pleasingly surreal is quickly punctured by the frighteningly violent. What is so astounding is the play's capacity to put you right there, in the midst of the fun and games, and the sudden terrors, of the psychotic mind.

The original staging of the play was a co-production involving the Edinburgh International Festival, the Tron, in Glasgow, and Plymouth's Drum Theatre. In reviving it with the same cast and creative team, the NTS is indicates its heartening intention of sharing the best of contemporary Scottish theatre with a wider audience.

Theatregoers in Dundee, Edinburgh and across England can expect a piece every bit as entertaining and affecting as the production which, deservedly, swept the boards at the 2004-05 Critics' Awards for Theatre in Scotland. Neilson, who directs the piece (as he did three years ago), has kept the show as chaotic-yet-disciplined as it was when it was first staged.

The uniformly excellent cast is led again by Christine Entwisle, who plays Lisa as if she were an alternately confident and petrified tightrope walker; at one moment joyously, dangerously free, at the next utterly fearful of her lack of self-control. It is a performance of intelligence and empathy, which is complemented by the riotous abandon of the other actors.

In the consciously slow-burning second half we witness Lisa as she is medicated in a hospital room. Nurses come in and out, ensuring she takes the powerful medication which suppresses her psychosis (but also numbs her consciousness). Doctors (never the same one twice) pay brief visits. Exasperated loved ones arrive, low on sympathy and unable to contain their feelings of powerlessness and anger.

My response in 2004 was that the second half was too polemical; the medical professionals seemed too stereotypical and Lisa's sister and lover both appeared unconvincingly harsh. Upon seeing the play for a second time, however, I now consider that a misreading.

The play's conclusion is neither naturalistic nor is it condemnatory (unless it is a general condemnation of a still widespread fear and ignorance where mental illness is concerned). With its distancing glass panel separating actors from audience and the deliberately alienating use of microphones, it is reflecting upon Lisa's hospitalisation from her own perspective. In a curious sense, the first act (in which Lisa is not on drugs) is more naturalistic than the second (in which she is doped to the eyeballs).

For those fortunate enough to have seen Dissocia first time round, this revival is a reminder of the heights to which Neilson's imagination can soar, and reveals new layers of subtlety in his exceptional script.

Those coming to the play for the first time can thank the National Theatre of Scotland, which has shown great judgement in giving a new life to this superb play.