If you're in your teens the original mass effect trilogy, from the storytelling to the going through the different genres of games

Explorations into Microtonal Tuning is a trilogy of albums by King Gizzard and the Lizard Wizard that follow on nicely from eachother, all very good albums in their own right, and a third thing I can't think of but would sound rhetorically complete.

Matrix 1-3

The 4th one doesn't exist in this house

croissant, butter, jam.

Movie trilogies: Guardians of the Galaxy, Tom Holland Spiderman, Deadpool.

Some people will disagree, but this is the closest perfect trilogy that I remember to play.

Danganronpa 1, 2, V3

Everyone's giving you answers you already know about because it's all pop media, so here's one you might not know. The Psychomech trilogy by Brian Lumley!

It's kind of a power fantasy type of read, but very entertaining.

Bonus Lensman series. It's not a trilogy though.

The original Crash Bandicoot games for the PS1: while the 2nd is the best of them all IMO, the other titles are so good that they created out of nowhere one of the most revered PlayStation mascots

Hard science fiction: Red Mars, Green Mars, Blue Mars by Kim Stanley Robinson. What would terraforming Mars be like?

Video games: the three Castlevania games for Gameboy Advance, and the three for Nindendo DS. Not trilogies per se, but they came in threes :)

vinegared rice, fish, soy sauce

compliment sandwich, dislike/criticism, compliment sandwich

homecoming, far from home, no way home: ymmv, nanotech spidey is just a fresh take imo

dragon quest: "castle in the sky" trilogy

beef slices, onions, rice bowl

His Dark Materials. Best series I've ever read, at all.

Dark souls

First 3 Fatal Frames.

And Portal. Even if there's only two, they were great lol