Great Question! I'm a pretty big gaming collector so rather than having a favourite game, I have favourite series but I'll include some newer genre stuff as well, here's my top 10 in no particular order:
1. Legend of Zelda Series (Nintendo) Massive fan, Breath of the Wild and Wind Waker are probs my 2 favs
2. Starfox Series (Nintendo) Again Massive Fan, Starfox Adventures could be my #1 fav game
3. FIFA Series (EA Sports) I play this too much lol
4. Fortnite (Epic Games) Yes it's a hype train but I play so much with my friends and it's provided a lot of entertainment so defs has to be included.
5. Super Mario Sunshine (Nintendo Gamecube) This is an amazing game, highly recommend, Mario Odyssey is also very similar
6. Super Smash Bros Series (Nintendo) So much fun, Melee is still my favourite but with Smash Ultimate coming out next week, that could change!
7. Pokemon Series (Pokemon/Nintendo/GameFreak) Amazing series and countless hours of adventure. Pokemon Colosseum, X/Y and Black/White are probably my favourites.
8. Kirby's Air Ride (Nintendo Gamecube) This is 100% a hidden gem and one of my all time favs. Everytime I get someone to play this for the first time, they love it.
9. Starlink Battle For Atlas (Ubisoft/Nintendo) I played this on the Nintendo Switch due to the Starfox special missions and story and man it was great. Definitely designed towards a specific audience but I loved it.
10. COD Franchise/Battlefield Franchise. Even though I don't play shooters that often anymore, I have so many memories from MW2/MW3 and Battlefield 3/4. Still will always cherish the moments I had with friends.