I find this DLC immensely frustrating and mostly just play with it off. As much as I love monster prom, everything added by this DLC apart from the secret endings (which, unfortunately, are good) detracts from the playing experience.
Before I get into the bad, the good: Dahlia, The Slayer, Cal, Miri, The Interdimensional Prince and Dmitri's secret endings are wonderful and an exciting extra selection for playing through. Good art, good stories, good fun. The couple showing up at lunch are pretty funny, if scarce, and if this was the entirety of the dlc it would be a strong 4/4.5 out of 5.
The worst of this mod is Leonard, and everything about why I find him frustrating has the same symptoms as my other more minor gripes. Leonard is a new side character antagonist, who is a typical obnoxious gamer gate type reactionary. He is openly misogynistic in a much more real and less cartoonist/trope-fuelled way than say The IDP or The Wolfpack, and he shows up throughout events to say something truly awful and get shot down by the player. This is, on the face of it, supposed to be fun and funny, and I believe it is because the writers are the kind of people who think that retweets to dunk on are the funniest and best thing in the whole world. Never mind that your game has to write in failure states, where you don't manage to shut him up and he continues to spout his awful opinions but now it's your fault. Never mind that your players now have to sit through "yes, there are people out there who hate you" when they're trying to relax and play a fun party game. Never mind that the jokes aren't even funny! Leonard single-handedly makes this DLC not worth touching.
My gripes around Leonard unfortunately extend to the way the game treats Zoe, the second DLC love interest. Zoe is a former eldritch being that has given up on that in order to become a normal(ish) high school girl. That framing is then used as an extremely shallow metaphor for transness within the game. Zoe is treated almost entirely like a trans woman - for example, Vera makes a comment that she's her sister, not her cis-ter - but without ever explicitly saying that she is trans. This cowardice and choice to make Vera explicitly cisgender would be enough to mildly annoy me, but the game also struggles to explore Zoe's transgender experiences through anything other than showing off the difficulties she faces. A large enough majority of Zoe's events feature Leonard appearing to tell her that she's not a woman that it is incredibly unlikely to complete a run dating her without him showing up. The player character, as usual, then has to defend her from him and make him go away. Yes, trans people get bullied, but it is both incredibly out of tone with the rest of the game and not fun to play, as a trans person, or even I imagine as a cis person who cares about trans people at all. Zoe doesn't even get a secret ending where she gets to just be unquestionably happy. Her first secret ending deals with her cult, who are a metaphor for a trans persons family, struggling to accept her as her new self. Her second secret ending is just more bullying from Leonard! It's lazy, not fun, not reflective of the trans experience, and overall I think is informed solely by the impression you get of trans people following the same people who love to quote tweet and dunk.
Zoe does not even have much redeeming her as a character. Zoe's primary character trait is that she loves fanfiction, and she particularly loves writing fanfiction about the other love interests at spooky high. She enjoys telling people about this and quizzing them on niche aspects of their personality so that her fics can be more realistic. This is all treated as very stupid and silly. Pointing at your target audience and telling them that enjoying your product is bad is rarely a move that makes your product more fun and this is no exception. Additionally, Zoe writing smut about the other characters and telling them about it explicitly makes the majority of them very uncomfortable. In a game where all the other love interests say a wide variety of zany and very horny things to each other and it is treated as cool fun and sexy to have the transgender woman love interest do it and it is treated as weird and off-putting is blatant transmisogyny. The easy and funny fix to this would have been to simply make everyone into it, but this game chooses not to do that (note: this context is also why the wolfpack does not work as well as a villain without some heavy gesturing at tropes, because with the in-univerae rules what he does and says is broadly very okay). I also don't like that Zoe was previously a monster who destroys the world in one of the games previous very few number of bad endings. Making trans woman before transition out to be monstrous (in a way that goes far above and beyond the monstrousness otherwise on display at monster high) only really serves to reinforce gender essentialism.
All of these negative aspects are why I leave the dlc off most times I play this game. It's difficult to leave a star review here, because it's pretty split between 0.5 stars (the stuff I detailed) and 4.5 stars (the stuff I covered at the start, and the wolfpack/dahlia lunchtime event). Overall, I've given it one star because I think your dlc has overall been a failure if it's better to leave it off than on when playing your game.