I'm more interested in the subject than the writer. O'Neill was the leader of the Irish side in the last struggle between the old Gaelic order and the London government; surrendering after nine years of war in 1603, he slipped away to exile in Rome and died there. For O'Faolain's purposes, he is of course a hero in that he tried but failed to establish an independent Irish state. But there were a couple of interesting slants which prevent it from being a hagiography.
Hiram Morgan has disproved one of the key planks of O'Faolain's narrative, that the young O'Neill was fostered in England, and Morgan is rather better on the overall politics and culture of the era. It's a bit of a shame, actually, because O'Faolain is big on the importance of communication and even compromise with the English, and O'Neill's (fictional) early life in England equips him to be the right man for this job. Where O'Faolain does better than Morgan is on the human level. His sixteenth-century Ireland is a rather sexy place (certainly in comparison to the repressed de Valera / McQuaid state). O'Neill's marital history is explained in great detail, including the elopement with Mabel Bagenal, the daughter of one of his regional English rivals. O'Faolain is fairly neutral rather than scandalised about this; I guess that he hoped his readers would draw their own conclusions.
And his account of the end of the war is rather good, though here he does slip into moral lessons from history a bit. Though a proud Cork man himself, O'Faolain admits that Kinsale was practically the worst place for the Spanish to land; had they come anywhere in the north or northwest coast, O'Faolain reckons they would have won the war fairly quickly. As it was, a less good English leader than Mountjoy could easily have screwed up the siege. But it's impossible to find a positive description of the way the arriving Irish soldiers blundered into a catastrophic and decisive defeat, and O'Faolain goes into splendid descriptive detail about it. O'Neill is in the end the victim of a bad Spanish decision, unusually good English command, and a lack of discipline among his own supporters and allies. My memory is that Cyril Falls, writing only a few years later and as an avowed Unionist, is actually a bit more even-handed in his assessment.
Anyway, not an essential book for historical understanding of the period, but an important book for understanding more recent perceptions of the events. And quite a good read.