Yeah, I put 'serious' but it's a crude guide.
I probably have a couple of dozen books now, often indie games which only have one book. I don't collect or buy for the sake of buying - I only buy a game now if I'm fairly sure it will see play... which requires my friends being into it as well as me and us finding the time to devote to it.
I do very little prep, and put very little thought into settings or campaigns prior to GMing. Maybe an hour - sometimes over a beer as we sit down to play. I may create a npc or two, or just envisage the key aspects and characters and relationships in a pirate haven. My game worlds are sketched by the players and then fleshed out by me at the table as the players interact with them.
On the other hand... I've been a gamer for 30 years, played and run countless games and systems. And rpgs are just one strand - even now a gaming session is usually an all weekend deal which will feature an RPG as well as Netrunner or Game of Thrones, Innovation, Mage Wars, Elder Sign or Spartacus or Red November.
I sometimes teach friends more weighty games - Twilight Struggle, Sword of Rome, Napoleon's Triumph, ASL. I may take some 1/1200 scale Napoleonic ships or 1/4800 WW2 ships and some rules and a blue cloth and get people playing Seekrieg V or Signal Close Action. And I'm happy solo-ing board wargames although it's an occasional thing.
So somewhere between 'serious' and 'very serious' I'd say. I don't have a single-minded focus, but gaming - as in role-playing, boardgaming and wargaming - is a consistently rewarding hobby.