Never seen Pretty Little Liars before but I tried this since I love slashers. Original Sin is campy, self-aware, and surprisingly well written. Each of the main characters has a distinct personality, with distinct flaws. There's so much unhinged behavior, coupled with pop music and cleverly framed shots. Karen, in particular is the most hilariously deranged character in the cast.
This is much more of a spiritual successor to Scream than Scream 5 was. It references modern horror flicks and filmmakers in a comical way. It's clear the directors have an understanding of their horror influences in the cinematography techniques. They never shy away from showing gory gruesome kills.
I loved the callbacks to Nightmare on Elm Street's school dream sequences. The creepy background music and handheld camera during these scenes really sell the scares. The few jump-scares it has are mostly well done, where it succeeded more was the psychological horror.
Acting-wise, not top notch, but they're talented enough to deliver at key moments. My favorite part of PLL: Original Sin is the one liners, "Fincher, Zodiac. Don't." was the best one. If you absolutely despise Zoomer words and phrases, just don't bother, but I largely think they approach the script with self-awareness and the over-the-top delivery implies irony.
It's shocking, funny, and most of all, scary. Give it a chance even if you're not a fan of the original.