These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Awesome Music: "I Can See Into Forever", the ending theme of the Blackwell Convergence.
Harsher in Hindsight: The appearance of Madeline in Lauren's dreams becomes more ominous when you learn in Epiphany Maddy will use this mental link to try and possess Lauren, driving her insane in the process, and has already done the same to Patricia.
That One Puzzle: Every game has at least one. Special mention goes to the "poison the dog" puzzle in Legacy, the "appreciate art" puzzle in Convergence (especially as you don't know if you've made all the right choices until the end), everything you need to persuade Jamie in Deception, and any puzzle that requires Joey interact with things, as 99% of the time using the interact command with him results in some variation of "I can't touch that, ya dingus".
Though you can get some advice on how to talk to Claude in Convergence by Oogling "Artists". Of course, if you haven't gained access to Meltzer's e-mail account by that point, good luck knowing that.
Rosangela's life is a never-ending parade of constant misery getting dumped on her. It's incredibly telling that being permanently bonded to a sexist, condescending ghost and being forced to help restless spirits move on was a positive influence on her life.
Jerkass Woobie: Several ghosts are this, or try to invoke this. Joey in particular seems to fit the trope, due to his persistent alternation between snarking at his medium and whining about his death and past experiences with the Blackwell Family.