[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...

[ojii]

Yes it's one of those "funny" words in Japanese that is highly context sensitive, so you're probably right.