This discussion may contain spoilers!
The reviews I've found, barring one (Total Gaming Network) echo what most of us have said - fantastic episode, with a few flaws it inherited from Launch of the Screaming Narwhal.
This one review rips the episode to shreds, thinks the merpeople were a bad idea and gave a poor score of 6.9/10. Feel free to read it for difference of opinion. and pour forth your complaints here