This game starts off awesome and somehow manages to get even better as it goes on. First off, it's so authentic to the music scenes it's portraying; the atmosphere of the concert, the observations of how certain fans of different genres act, an entire D&D board designed as a tribute to a band, there's a lot to like. The author clearly knew a lot about the subject matter and pulled off a great tribute to it. Some of the purist jokes and elitism almost definitely come from experience (“I didn’t say The Warning—you know, the extremely-popular-femme-fronted Mexican hardrock band—I said WARNING, whose 2006 album, Watching from a Distance is one of the bleakest, noisiest doom-metal albums of all time!").
The game's puzzles are based around an evolving mechanic where you recruit your bandmates, who are preoccupied with activities from evading stalking fans to being caught-up in a game of Animal Crossing. Once they're on your side, you can jam with them to use their types of music to your advantage, each portrayed in a clever manner: sludge metal causes grimy water to pool and pirate metal summons seagulls, for example. Merely by the way Codex Sadistica describes the music do you get the full impression of what it would feel like to listen to, and that's very impressive writing.
If you have at least two band members, you can have them jam together to make new genres of music. You get a lot to do using these, and I had a lot of fun seeing what kinds of music I could make and how it would solve the puzzles. The game has a good amount of hinting for which genre would be best or what order you have to play in, so the puzzles never feel unfair or too niche.
I was genuinely hyped throughout the entire climactic battle. You (Spoiler - click to show)light the stage on fire and fight off the demon form of a glamrock vocalist, finally unlock Mae's full potential with her drumset, and get to play even more powerful genres than anything you did before. The entire thing is fast-paced, thrilling, and a natural ending point of everything the game set up. It closes with the band all playing in unison as you prepare to do what you do best: scream. Cut to the victory screen. It's perfect.
Codex Sadistica takes a theme that's not usually seen in IF and executes it with so much passion. The writing is amazing in capturing the harsh atmosphere of a metal concert and the characters all have their own unique personalities that make reading their dialogue enjoyable. The core puzzle mechanic is well-implemented and constantly evolving, with a lot of genuine tests of how well you understand it. Even if you're not that familiar with the music scene it's referencing, it's a very well thought-out game that you can have a great time playing.