90% of Mario games range from either pretty good to... atrocious. A large part of this 90% is consisted of spin-offs like Mario Party. Only 10% of Mario games are deserving of the legendary title.
I noticed sort of a downfall in franchises. The more installments, the lower the aggregate review scores. But then there's Zelda. 19 years after the Zelda series' debut... TP comes out with the second highest ratings of the entire series. Now that is called consistancy.