I have "Monsters" on right now, and this episode is not bad!  Great showcase for Orla Brady.  Some good Seven/Raffi moments.  Though I do love a Trek "Odyssey Into The Mind", I'm almost never disappointed by that trope.  Only DS9 "Extreme Measures" comes to mind as a letdown.
The Rios thread in this one is impossible to defend, though.
And I suppose even mostly liking it, I would still rank it as the second weakest S2 episode.  I would only put "Mercy" below it.