Comment by iterion1

Could also be 'surprising'. With the context of the sentence before it is basically, "I thought this would be hard to write. Ruby is surprising."

Also, the author is a contributor to ruby on github, so I doubt he is negative towards the language.

http://jisho.org/words?jap=%E6%81%90%E3%82%8D%E3%81%97%E3%81...