George MacDonald was a good thinker in some arenas, but he was a universalist, and not solidly biblical. However, C.S. Lewis said George's books baptized his imagination. Lewis's baptized mine.
For more information on universalism and the doctrine of hell, see http://www.epm.org/resources/2010/Feb/4/wouldnt-loving-god-let-everyone-go-heaven/
http://www.epm.org/resources/2010/Feb/2/why-im-big-fan-hell/
http://www.epm.org/resources/2010/Feb/22/gritty-reality-hell/