First off, it's not a look at any Irish Empire, but an examination of the Irish Diaspora. Nor is there much meat there, as the focus seems to be much more on how those poor emigrants must have felt, with much less information on what they did.
Presented in a scatter-shot time-line, jumping from the USA to the Irish left behind in Ireland, to India where the Irish were the mainstay of that awful Imperialism, to Australia where there were some success stories, to the poor, powerless Irish women whose story was never told (which they bewail repeatedly, without ever trying to tell that untold story).
There were some good tidbits in there, but all in all, it's more bewailing the 'Irish Tragedy' and less a history to learn anything from.