EVs don't exist as we know them now. You could get maximum of the then EVs in every stat, so everyone was just bulkier in general.
The special split and fixed mechanics, and new Pokémon like Skarmory and Blissey made defense much more viable, especially with held items, since Leftovers was far and away the best.
Snorlax had it all though. With the special split, he had a huge new special defense stat and access to the new TM for Curse, which was perfect for a high HP, high attack, high special defense, slow Pokémon like him. Body Slam and Shadow Ball had amazing coverage against everything that wasn't Skarmory basically, and he hit like a truck. With lefties and RestTalk, if you couldn't kill him in three attacks, and you probably couldn't, you couldn't kill him at all. He also had a powerful option of running a Belly Drum set for sudden PANIC wallbreaking as well.
Heck, half the reason Skarmory was good was because he could whirlwind out Snorlax, wall him, and get residual damage with spikes, and even that failed if Snorlax was the last Pokémon standing.
Both offensively and defensively, he could clean things up or be an immovable mountain to block his opponents. The undisputed king of GSC.
