This game could be fucking nearly COMPLETED if not for all the side story bullshit. Each and every render of some crazy unknown character doing some dumb shit nobody cares about is a render taken away from characters we interact with and care about... Imagine if other games did that shit really imagine it...
To me, the biggest problem with the side story was that it was poorly implemented. There were a lot of threads tying Manston in general to the criminals that
could have made a stronger connection and made things more interesting. But the ties were, as you mentioned, to characters less cared about or not even appearing in the rest of the story. If I had spent more time getting close to Isabella, I
might have cared about what happened to her mom. (Hell, either Isabella hadn't heard or she herself didn't seem to care.) If there were something more with Jessica, I
might have cared that she was in the coma; after a while, I almost forgot about her completely. If I got attached to Mrs. Miller (and not just gotten blue-balled twice), I
might have cared about the attack where Alyssa worked.
I don't think all of the side scenes were bad, either. I just think they were misplaced within the story. There were too many too soon, before any real attachment to the characters we
did follow was established. With Alyssa, for instance, we only really learn why she goes out late at some seedy night club
if we happen to go downstairs the first night at Mrs. Miller's, instead of waiting like she asked. We don't follow Alyssa's story enough, though, to get attached to her. Sure, we "rescue" her while out on a date with Mercedes and put her semi-conscious ass to bed, but there's no real time spent with her or her mom to build the kind of connection needed for the attack at her work to be anything more than a plot point.
While I do agree with White Phantom that there were too many things going on all at once, I think the
result of that is the biggest problem for this game. It's a similar problem to what franchises like
Star Trek run into: there are too many characters to control. With large ensemble casts, you generally have three choices: (1) they can be put into a lengthy show format, like a graphic novel or television series, where each character can get focus in individual issues or episodes, building our connection to each over time; (2) the creator can focus on a limited number of those, relegating the others to side / background characters; or (3) the creator can try to give them all equal focus, which
almost always ends in shallow characters, so people tend not to care about any single one of them very much.
The latter of these is what's happened to
Shadows over Manston. While there were definitely certain characters the carnal side of me wanted to sidle up to (OK, more than just "sidle"), I wasn't invested in any one of them really, even when I specifically made choices to give them more time.