Another classic horror plot, and there's nothing wrong with that. The classic plots are classic for good reasons, and it's the execution that matters. I enjoyed seeing the famous ACD fairy photo used that way.
Introducing a character important to Jack's life only to kill her five minutes later is, um, well, frankly, it's one of my signs of bad writing. Payoffs are more powerful when they are separated from their setups. Set up Estelle in this ep, kill her off three eps later (or a whole season later), and it means something. As it is, cheap attempt to tug my heartstrings that is meaningful to the writers only as a vehicle for Jack backstory revelation. Bah.
Husband says that it felt rushed to him.
The Lahore 1909 incident is interesting. Was he American? Or are we supposed to read him as British? (What would American troops be doing in UK territory?) How old is Jack supposed to be in the American military records in WWII? Estelle thought he was 30-ish. And I note that Gwen has twigged, which is good, because otherwise I'd begin to worry about her.
ETA: So I suppose how I'd summarize it is: We were interested in the monster-of-the-week plot, and we were interested in Jack's backstory, but the two were not meshed well. We'd like more of a sense of an overall plot arc, or the sense that the writers realize they can delay their payoffs. The series could yet give me all that, but I'm not yet certain it will. My trust in the writers is still developing.
Is all television going to be disappointing after Joss Whedon?