I can narrow it down to ten, but I can't get it smaller without just going with a top two. Also, beyond those top two these are not in order.
Chrono Cross: Basically everything about it. I love the world, characters, story, music, visuals, enemy designs, etc.
I love how unique the combat feels and how well it works. I love that there's so much content and you can play it a little differently every time. I love the little touches that show how much they cared, like the custom frames, characters having unique accents in their dialogue text, etc.
The only thing I'd change is I would make the New Game+ cycles increase in difficulty.
Bomberman 64: It's probably the most charming game I've ever played. It's a super unique take on a 3D platformer with a lot of variety in the way to play it and solve puzzles. I also just really love the character designs and the boss fights.
Resident Evil 4: It's so insanely fun with tons of replay value and plenty of gameplay variety to keep it interesting. It's so bizarre thematically, taking you from a run down village to an old castle, it's almost like every main area shifts genre a little bit. The gameplay is super fun, especially on Wii, and the mood is just the right mix of horror and humor. Yeah, it's a pretty notable departure from previous games, and I love the classic entries, but this is just too likable to give up.
Also, the little things. The merchant, the shooting galleries, the Mercenaries mode... there's just so much to this to love.
Symphony of the Night: This one's weird, because objectively I think at least a good number of Castlevania games are objectively better... but between nostalgia and just the way Symphony specifically feels and plays... it'll always be my favorite in the series.
But this game is a blast to explore. There's so many little secrets and tricks to it. It's always enjoyable to explore the castle; even the backtracking is interesting because you're regularly unlocking new paths. The RPG elements are a really great touch to keep the gameplay interesting, and there's so many rare drop items that it gives a ton of replay value. Then the SECOND castle. Like... when I saw this game was 'near the end', only to find out there's an entire second castle secretly hidden behind cryptic riddles? Still one of the coolest moments in gaming for me. I also always loved "upside down" topsy-turvy style areas in games, and this entire castle is that.
Banjo-Kazooie: Insanely charming and just so much fun to play, I really can't think of anything wrong with it. It's like... a perfect game. It's genuinely hilarious, too. So many memorable and fun levels to explore, so many interesting characters to meet, and always something new to the gameplay. The final boss is a board game! Also, Game Over Gruntilda... c'mon.
Final Fantasy IX: This game has Vivi in it. I could write out a paragraph or two about how much I love the characters, the story, the world, the gameplay, the humor, how insanely dark it is, etc... but all I really need to say to get my point across is; Vivi's in it.
Soulsborne series: I can't... choose. Excluding Demons' Souls and Elden Ring, which I enjoy but are definitively my least favorites... I cannot pick between the rest. Each one has SOMETHING that I love it for enough to put it at the top...
~Dark Souls 1 has an amazingly well designed world with very well thought out level design, the lore is really interesting and fun to piece together, it has spectacular atmosphere, and I love its sense of methodical combat. It also has some of my favorite areas in the series.
~Dark Souls 2 lacks the quality of the previous games, but it just has such a massive variety of playstyles and replay value. There's so much content here, the DLC's are a huge step-up in quality from the base game, and it has some realy, really good later game bosses.
~Dark Souls 3 has some of the best bosses in any game I have ever played. Yeah, most of the earlier bosses are pretty weak offerings, but when you get a bit further in...
~Bloodborne has such a cool theme and concept behind the world, with really interesting lore and some of the most memorable characters in the series. It brings back the world design quality of the first Dark Souls, but also started the trend of amazing bosses that DS3 would inherit. Trick weapons are such an interesting idea that make so many weapons genuinely fun to use, and several of my all-time favorite weapons in gaming are here. It also does atmosphere exceedingly well. Shame about the Chalice Dungeons...