Cuchulain seems to be a far more popular subject of modern fantasy drawing from the Irish legends than Finn MacCool. In fact, I can't remember coming across any other version of the latter apart from Lady Gregory, who I must have read over thirty years ago, and I must admit I am hazy on most of the details.
This is a fairly fat novel, dealing entirely with the boyhood deeds of the hero and concluding with the only incident I can remember from the original legend (the cooking of the Salmon of Wisdom). It is a good effort, a Bildungsroman about a character with superhuman powers, and with unusual care taken to avoid anachronism - no Christian-era personal names, no potatoes, not too much wishful thinking about how perfect and emancipated pagan Irish society was. I enjoyed it more than I had expected to.