Bizarro Episode: The Winchesters have never so much as mentioned Chicago again despite the fact that this episode introduced the idea that Chicago is teeming with powerful monsters. Considering that the Winchesters spent all of Season 7 trying to rid the entire U.S. of Leviathans, it seems odd that they wouldn't take a second crack at cleaning up Chicago.
The general complaint surrounding the episode was that most critics felt that the episode was just recycling the concept of Season 1 with the main protagonist being driven by the murder of his girlfriend, then the plot involving his missing father. The fact that the character was too bland to even carry the whole episode by himself didn't help either.
They Wasted a Perfectly Good Plot: Concept-wise, the potential is there and could have been better with a little polishing. Also, it would have been better if it weren't in the same universe as Supernatural as the episode opened a lot of plot-holes.
Taking the concept into consideration it would have made a good arc for The Winchesters to handle and a nice breather from the Heaven And Hell arcs that plagued the series as of late.
Vanilla Protagonist: Ennis as a potential main protagonist was pretty bland and the bulk of his arc being ripped from The Winchesters arc in season one just made him look even less unique in the process.