My top favorite events:
1. D.D Castle
2. Turbo Duel Grand Prix
3. Special Duel Highlander Format
The events that I most hate:
3. Raid Duel
2. KC Cup
1. Duel Carnival
What's yours?
I started to play at December 2018. I remember a Special Duel event that we should play with decks containing a certain number of cards according the characters we played. Just like the decks from anime.
Monster World event was like a tabletop game where we walk a map, find treasures, monsters from cards and fight bosses using thematic decks they let we choose.
Its PVP vs PVE after all.
At very least you could face a different set of deck in PVE ( and sometimes developing a new combo for specific enemies), while PVP mostly consist deck you are familiar with.
Gladiator Island and Monster World is like playing RPG in DUEL Links.
Tabletop is like playing Duel Links with storylines.
Developers back then are very motivated and have brains.