I downloaded this for free from Amazon. Based on the cover, I assumed it was meant for children, but the target audience seems to be more Young Adult.
I'm not generally a big fan of time travel adventures - I've read the paradoxes enough times that I don't find them intriguing anymore. Happily, Mr. Fish does away with most of that element with some simple handwaving. Instead, he focuses on the story - the time machine is more of a Connecticut Yankee-type of gimmick. It's a wise decision, and Mr. Fish has fun with it. His writing is smooth, and his characters engaging.
Unfortunately, Robin Hood is as tired a subject as time travel, and Erasmus' slapstick escapades simply don't breathe enough life into the story to carry it along. In fact, I found a distinct Hollywood flavor to the book - as if it were designed for video rather than prose. The author also sometimes skimps on credibility in favor of fun - perhaps a little too often. It's a bit surprising in an author who clearly knows his period fairly well.
All in all, it's a pleasant story, and Mr. Fish is clearly a good writer. I wish that he had found a more interesting and original plot to apply his skills to. But if you aren't yet sated with Robin Hood, this is a fun way to get some more.