BLACK WATCH, THE MOST ACCLAIMED PRODUCTION IN THE NATIONAL THEATRE of Scotland's two-year history, has returned home following tours of duty in the United States, Australia and New Zealand. In the 20 months since John Tiffany's production of Gregory Burke's play took the Edinburgh Fringe by storm, the show has received almost as many awards as its eponymous regiment has won battle honours.

Watching its return to Scotland, it wasn't difficult to see why the drama has become such a theatrical phenomenon. The Iraq disaster continues to occupy the public consciousness. Now, as in 2006, the play's portrayal of former Black Watch soldiers recounting their experiences of Iraq in a Fife pub carries the stamp of authenticity.

The latest production is little changed from the winning formula which made the show such a hit in Edinburgh. Inevitably, however, the cast has altered significantly as the piece has gone about its travels. Brian Ferguson (brilliant as disillusioned squaddie Cammy in the original production) left the cast some time ago; despite the best efforts of Paul Rattray in the role now, one feels Ferguson's absence. Michael Nardone is an interesting addition to the cast; the muscularity and sarcasm of his acting are perfectly suited to the role of the gruff sergeant, but it seems almost gratuitous to ask him to also play the mild-mannered writer.

Despite the changes in personnel, the 2008 incarnation of Black Watch is as affecting as the first. Indeed, watching the drama in Glenrothes, in the heart of the Black Watch's recruitment area, was particularly poignant. The play's most powerful moment - in which we see the immediate aftermath of a suicide car bomb - is based upon a real attack in which three Black Watch soldiers from Fife (Private Scott McArdle, Private Paul Lowe and Sergeant Stuart Gray) and their Iraqi interpreter died.

We watch the three soldiers, bloodied and agonised, as they fall to the ground in slow motion. Their appalling descent is accompanied by a painfully plaintive Gaelic song, sung in beautiful, unaccompanied female voice. There is nothing in cinema which can touch seeing this incident realised so emotively in a live theatre environment.

Moments such as this account, in large part, for the success of Black Watch. Audiences still marvel at Tiffany's virtuoso touches, such as the moment when the action switches from the Fife pub to the Iraqi war zone as a soldier rips open a pool table with his bayonet and emerges in battle fatigues.

There is much more to the production than such spectacle, however. Audiences continue to respond warmly to the play because it humanises the conflict. From the reticence of the ex-squaddies' recollections of Iraq, to the heavy drinking and lurid banter which provide a thin mask for their war trauma, there is an undeniable truth to the play. Perhaps most memorable is the scene in which a former soldier cracks suddenly, threatening to break the arm of the playwright who is interviewing him.

Tiffany's production is a theatre work which has arisen from, and responded excellently to, its times. However, I feel now, as I did when it was first staged in 2006, that Black Watch is a very, very good piece of popular theatre, but not the enduring theatrical classic which the accolades have suggested.

It seems unlikely that people will, in 20 or 30 years time, be going back to the script of Black Watch in the way that they will return to the text of Gagarin Way, surely Burke's finest play thus far. The reason for that is quite simple: Black Watch is not a great work of universal metaphor, but a play of its day, given an outstanding production by an extremely talented director.

Nor is Black Watch particularly sophisticated in its construction. The script has a very discernible schema, which leavens the moments of sobering pathos with relieving comedy; it's an effective device, but not a subtle one. Steven Hoggett's choreography - with its over-long segments set to the excellent music of Max Richter - does not deserve the exaggerated hype it has received.

The production also lacks political courage. The overwhelming tenor of the piece (not least in the emails which a senior Black Watch officer sends home to his wife) is one of criticism of the politicians who ordered the Iraq War, but something dangerously close to glorification where the imperial history of the Black Watch regiment is concerned.

The famous "uniforms" scene (in which a soldier takes us on a tour of Black Watch deployments past) sanitises the dirty business of colonialism. If the play's international engagements had included Nairobi and Ramallah (where people remember the brutal events in which the Black Watch were involved), I suspect it would have received a less fulsome welcome than was the case in New York and Sydney.

In the places to which it has toured, however, there is no denying that Black Watch has struck a very definite chord with the public. The evidence of the Glenrothes performances is that this latest tour - which takes in points across the UK, as well as dates in Canada and the US - can only further enhance the play's towering reputation.

Black Watch is at SECC, Glasgow, Friday until April 18, then touring www.nationaltheatrescotland.com