Oh man the late 90s were absolutely killer! Although my pick was Pokémon Gold/Silver, I had to mention some others that just missed the cut in no particular order.
Unreal Tournament/Quake III Arena (I usually lump these 2 together lol)
Age of Empires II
Tony Hawk’s Pro Skater
DK64
Crash Team Racing
Pokemon though……I would hardly ever put those games down! No matter where I was. Even got the games confiscated at school several times xD one of my most nostalgic titles.