Not a minigame, but Maniac Mansion being within The Day of the Tentacle is probably my fav.

The full 4K version of Timesplitters 2 inside Homefront: The Revolution, but you have to play something like 75% of Homefront to reach it. I’ll reach it one of these days.

Probably not what you are asking for, but the character creation process in the Traveller ttRPG is a great mini game. You basically take a person from 18 to however old you want, and their life path is dictated by your choices and random dice outcomes. It’s a lot of fun. You can end up with a retired admiral, a prisoner or criminal, psionic, etc. Going through this process with a table of friends let’s you build in rich fun connections along the way. The actual RPG then starts with mature, connected characters with a history, instead of 4 randos meeting in a tavern. In the classic Traveller you can even die in character creation. Current iterations removed the death component but you can be maimed from accidents in your career and start the game with a mountain of medical debt.

The minigames in shenmue/yakuza. They are literally full games.

Treedude in superhot

And… Umm

Mario party

Caravan from Fallout: New Vegas has a notoriously bad tutorial, but is easy enough to grasp and fun as an early-game money source. Would have benefited from a Gwent-style sidequest chain.

Let’s be real, Witcher 3 is just a Gwent launcher.

Also I’ve definitely played more Pazaak than KOTOR.

Pretty much every minigame in Majora’s Mask is making you forget the world is ending

I thought of another one. There is a minigame in Xenoblade Chronicles 2 called Tiger! Tiger that is great. it is basically an arcade game where getting certain scores gives you credits that can be redeemed for upgrades for some characters. The minigame is randomized and has three different difficulty tiers and is overall really well done.

Not sure if it will count, but the Ancient Cave in Lufia 2 (SNES) was a game in and of itself. It was basically a roguelike dungeon. 100 random floors, it reverts you to level 1 and there were rare special items you could sometimes find in runs that could be brought back in. Beating the Ancient Cave is much, much harder and more rewarding than beating the game itself (storyline aside).

Ratchet and Clank: Up Your Arsenal had a side scrolling Captain Quark game that was quite good

The hunting game in Oregon Trail.

Playing Receiver in Receiver 2 was a fun surprise.

Didn’t rocket league originate from a minigame ?

Triple triad card game from FF8? Also the card game in FF9, I forgot which is which.