Absurdly Sharp Blade: This is what most people assume happened to the victims, even though it turns out they all exploded from the inside and an exploded person should not look the same as someone gutted like the catch of the day.
Badass Boast: "The wheels of justice may grind slowly, but they're movin', they're movin'. You get yourself caught in those wheels, Quinlan, you're in for a lotta pain."
Beneath Suspicion: It's hard to get more beneath suspicion than being in a coma! (A coma with brain activity that spikes whenever the Ripper kills, hmmm...)
Body Horror: The Ripper makes his/her victims explode from the inside.
Brown Note: Apparently in her spare time, Dr. Burton records the mental "death resonances" of monkeys she's tortured to death in cyberspace and sells them on the black market, for who knows what purpose.
Bunny-Ears Lawyer: Farley is a Fat Slob whose autopsy methods are...questionable, at best. He also comes up with a viable lead on how the Ripper kills from afar.
Digital Avatar: Quinlan's is a simple-looking green putty CGI man that absorbs software into its rubbery head.
Dirty Cop: Magnotta. He's not explicitly on the take, per se, but he's about as unethical as you can possibly get, seems more interested in covering up the Ripper case than actually solving it, and is one of the possible suspects.
Moon Logic Puzzle: The final puzzle of the game has you input a sequence of Tarot cards to receive the anti-Ripper weapon with no apparent clue to the correct sequence. However, during the puzzle "Don't Fear The Reaper" starts playing. You're inclined to ignore it since it's the game's theme song and this is the endgame...until you realize that the key to the sequence is the song's lyrics ("'Seasons don't fear the Reaper/Nor do the wind, the Sun and the Rain..."). While it's simple in retrospect, you're likely to get stuck since you're not expecting the sudden use of Painting the Medium.
Multiple Endings: Curiously enough, the identity of the Ripper is actually randomized at some point of the game, with some elements changing accordingly. Disappointingly however, the endings are mostly the same regardless of the culprit. It can be inferred that only one of them is the "true" ending, due to the way it's differently handled than the rest (and that that one person was the only one with a specific grudge against all the victims) but, again, unlocking that ending is randomized. It's likely the others were just thrown in at the last moment.
Not-So-Badass Longcoat: Quinlan, who's only journalistic credit seems to be printing the Ripper's letters, even his comatosed assistant is a much better investigator than him.
Only Smart People May Pass: The majority of the puzzles that make up the "hacking" minigames are either puzzles, or, bizarrely, first-person rail shooter segments.
Oral Fixation: Walken's character is chomping on a cigar in almost every scene he's in. Literally. Spoony explicitly points out "oral fixation" and adds a "NOM!" every time Walken chomps away at the cigar.
Police Brutality: Detective Vincent Magnotta has been known to beat confessions out of people
Solve the Soup Cans: Many, but one of the worst must be the set up in Catherine's apartment which involves crystals that must be put in a certain order in a grid that fires a laser at a book. You're only given a very vague idea of where to put crystals on a very specific grid to create a constellation, and the payoff is ultimately something Catherine could have just left you in a note: her password. Just to make it worse, the puzzle centers around the constellations of the horoscope, and the password is Horoscope, meaning that solving the puzzle means you have to already figure out that Catherine was interested in horoscopes, despite that information alone being enough to make a reasonable guess at the password.
Another infamously terrifying puzzle, one whose mere screenshot is used as a reference to how tough the puzzles in an adventure game could be, is the circuit board rewiring puzzle. It looks about as complex as learning how to solder chips in yourself without getting anything wrong would be in real life; fortunately, abstracting out some of the codes and what-not can make it easier.
Real Song Theme Tune: "Don't Fear The Reaper" by Blue Oyster Cult. The song's lyrics are the key to the final puzzle.
And Spoony learns the hard way that they too fall under Guide Dang It; in one of them, it's not enough to shoot the pop-up targets once, but to shoot them as many times as possible in order to get the qualifying score, even though the game fails to tell you that little detail.
Video Phone: Complete with Blue Swirly Thing in the corner.
And, as Spoony points out, it wouldn't have worked anyway.
Magnotta: Self defence, man. I mean, why'd you hit me, Quinlan? What are you, stupid? Hitting a cop?!
Spoony: With a knife, while handcuffed.
Your Mind Makes It Real: Forget hacking into the human mind to give you an aneurism or whatever: the Ripper can hack your brain in such a way your body's internal pressure builds until you explode from the inside.