This Pokémon series popularized Alternate Arts, which are uniquely illustrated versions of full art cards which display Pokémon in a variety of scenes and locations.

Sword and Shield
Vintage
This series brought back ex cards which were first introduced during the Ex Era.

Scarlet & Violet
This era features Gold Star Cards, which are some of the most sought after and valuable cards in all of Pokémon, for being printed not as much as WOTC due to lack of popularity.

Experimental Era
This series produced the Detective Pikachu set, which has cards illustrated based off of Pokémon from the movie.

Sun & Moon
This era contains the most diverse and assorted sets and cards, and superior in my opinion.
Experimental Era
As of Mega Evolution Phantasmal Flames, How many Pokémon sets have been made (excluding Pop Series, Topps Chrome, Energy Subsets, McDonald's Series, Trick or Treat Sets, Holiday Calendar Sets, and Promo Handouts)?
130!
This series features the most Charizard cards (promos excluded).

XY (14)
This era is wildly known for having many print errors, ink errors, and symbol errors throughout most of the sets.

Vintage
Hundreds of Artists have articulated and illustrated cards in this era.
What series features the most sets, being 17?

Sword & Shield
Vintage