Is it even a lil bit "dark" as the last 2-3 arcs with Yami Bakura etc etc or its just duels ?
It's plenty dark - just as dark as DM but probably better character writing
Like, in DM we had:
Pegasus: Oh no my girlfriend died, i must go exploring egypt... im back from egypt and have a stupid eye so now i have to 180 and become a dickhead
Bakura: possessed by an evil bandit spirit who hates puzzle man for no reason
Rafael: my sister died so now i'm going to blindly follow Atlantis Hitler
Dartz: I am Atlantis Hitler and want to resurrect the creature that destroyed my own civilisation because reasons
In 5Ds there's a lot more relationships with characters like Yusei, Jack, Kallen, Crow that are genuinely really fleshed out and fully explain the wrongdoings and goals people have in the show - there's also a lot of civil rights stuff involved in the story; genuinely interesting
But then the other shows should be avoided they're literally just:
GX - A school for a card game, gets invaded by and helped by Aliens because reasons
Zexal - Weird unexplained spirit must win cards through duels or he dies
Arc-V - Some circus dude finds out there's other dimensions - alternate version of himself wants to destroy the multiverse because reasons
VRAINS - VR meets skateboarding emo who gets hacked by an AI who specifically really hates one dude because reasons
Sevens - Dude invents a new dumbed down version of the game because he's a moron
Go Rush - The dude didn't actually invent the new rules, they existed out in space because reasons