What I loved about this specific episode was the imagery. I thought it was quite rich and I felt there was a lot of effort to make it really atmospheric. I liked that it tried to present the story from Ianto's perspective, but I do think that it felt very generic (a quick substitution of Gwen for Ianto and still have it make sense is not good).

I still think and like the idea that the story could be told from Ianto's perspective and trace his contributions to solving a case. It needs to commit to it, though. Really follow him, so we don't get conversations that Ianto isn't privy to (with exception of the baddie POV).

I do love this idea:

Jack hears spooky music in the Hub, asks Ianto WTF? Ianto tells him to STFU and hands him his coat. Jack and Ianto go to Electro for night out.

I think very much in character for Ianto and Jack. And you're really right about too much time is spent with Jack trying to be clued up.

Rewatching bits, Jack offers almost no information about his time with the carnies and no resolution to how he got out of being involved with them. That did bothered me. It's almost like there's too much material and they are trying to make the storyline believable in only a single episode.

Also, the whole "Ianto, I need your local knowledge" is really... it doesn't make sense. Ianto's been in Cardiff for how long compared to Jack?

So many nifty ideas, just not brought together well.

the resulting spookiness would have amusingly shown us how patently impossible it is for these two to keep their work and private lives separate

Yeap! It would make for an interesting contrast to Gwen/Owen last season.