Yes, HI lacked a plot in the common sense of the word. It has no clear begining, middle or ending. I think the point was that the story was supposed to emulate life in that way. Our lives consists of a string of events that most often aren´t connected.
Sure. But strictly IMO it makes for less compelling reading than the concept at first would indicate. It risks becoming too like one of those TV series that continues on and has to come up with new big unexpected twists and turns and cliffhangers as long as the ratings are sufficient.
I do think I reacted far more to the continuous big-time drama (the way I perceived it) than the meandering nature of the tale, actually. I though the dramatic events in HI were entirely unlikely to all befall one couple in a short period of time. While in TCJ things seemed to calm down to more closely emulate RL as far as the content of actual plot events and -development went. Both the daughter-turned-religious-zealot and the aging parents needing help seemed to be realistic and more low-key and to initially allow for that "similar to RL" approach (and depiction of related relationship closeness and -strains for J&E). That worked better IMO.
I think the reason I prefer ZatB to Hi, is that it´s darker, more complex and Doctor Jack and Hitman Ennis are closer to canon.
It's actually strange to note that the AU!AU characters seem closer to canon than the canon!AU characters.
My main objection to HI has always been the characterization of Ennis, who I couldn't recognize as canon Ennis at all, though that was supposed to be his starting point.
The depiction of the development of the ZatB relationship from the first meeting, the slow evolvement of D from completely closed-down to a loving partner in an openly gay relationship, the sheer level of angst throughout, the excitement fit to give a poor reader heart attacks, the focus on J&E with less interference from OCs, .... yeah, all the parts of ZatB just clik together into one whole that is larger than the sum of those parts and just appeal to me all the way.
As for the frequent and highly dramatic events in ZatB, they follow naturally from the very dramatic starting point and the crime/mob hit context of the tale - these two men are not exactly living ordinary everyday lives.