Its usefulness is slightly diminished with the release of The Book of Exalted Deeds as some of the concepts used in Unorthodox Clerics are addressed in it (although usually as a prestige class rather than a full class). Still, at only $2, its hard to go wrong with these even if you find the classes contained within only marginally useful. I thought the Elementalist was a unique twist worth the cover price alone.
[4 of 5 Stars!]
I am very glad you liked this book. Funny thing is that during editing I didn't care much for it at all, but the playtesters loved it. And now that it has been released it has gotten rave reviews! I guess the writer, Robert J. Hahn, knew far better than me!