This is a great question! I think it's a great question because there are a lot of people out there who are compelled to purchase an entire product line and don't consider the game "complete" without it. But there are some, such as myself, who tend to ONLY use the core books, and not only not use supplements, but more often than not I ban them from the table ("If I haven't studied it, you can't use it!" is a policy I normally carry at the table, particularly for supplement-heavy games like prior editions of D&D). My philosophy on it is this: the more books, the more shit I have to cram into my head, and consequently the more variables I have to account for when actually playing the game. There are a few games where this is so true it hurts (read below).
This extends to boardgames for me, as well. Though there are a couple that I deem essential (I really like Scoundrels of Skullport, for Lords of Waterdeep), I'd rather invest that money in a whole new game.
Come to think of it, I'm that way with DLC in videogames, too. Just the other day, I was pondering between the new expansion for Call of Duty: Advanced Warfare (super-soldier zombies!!!) or Evolve. Even though Evolve was more expensive, I choose that, because I wanted a different experience.
As you can see from the example above, money isn't often the issue with me. It's more about the experience. I can totally understand a cash-strapped gamer wanting expansions over new stuff because he wants a guaranteed good thing, but even in that scenario, I'd often rather buy a new cheap game than a comparably priced expansion for one I already have. I understand that's just me, though. Overall, I think it's pretty cool that the entire gaming hobby has this ability to grow vertically as well as horizontally.
Anyways, I'm a tabletop roleplaying gamer, first and foremost, so here are my five picks for "most independent" RPGs:
1. Fate Core: I actually think this game is best when you try not to overthink it and just roll with it!
2. Dungeon World: Same as Fate Core.
3. Warhammer FRP: The majority of this game's product line is adventures, so a creative GM isn't missing much at all! A similar argument can be made for the Star Wars games, but less so as those games have sourcebooks for their various careers that probably drive a completist crazy.
4. 13th Age: "The anti-D&D," this game is practically built on the concept of needing as little extra crap as possible!
5. Numenera: Similar to 13th Age, this game is built on creativity, not comprehensive book collections. Ironically, though, there is a lot of stuff already available for this fairly-new RPG.
And, yin to yang, here are my five picks for the least self-contained (most-sourcebook-dependent) RPGs I've ever played:
1. The One Ring: It's a relatively new system, so there aren't too many books for it, but I can't imagine extended play of this game without at least the setting books (Heart of the Wild, Rivendell). The special dice are a compelling purchase, too.
2. D&D 4th edition: Though all editions of D&D are pretty sourcebook-dependent, 4th took it to the next level with its paradign-shift to a more tactical game. Any RPG that has three Player's Handbooks and two Dungeon Master's Guides is a game made for deep pockets and wide bookshelves!
3. GURPS: In theory, the 4th edition corebooks have all the rules. In practice, however, a game group's going to want to have any and all supplements pertaining to their particular campaign world which, depending on that world, could extend to several different titles. I had a respectably-large collection of 3rd edition stuff back in the day...and I never used it once.
4. Rifts: This game practically invented the idea of "splatbooks." Same can be said for almost every game from Palladium books, as well.
5. Shadowrun: There's so much stuff crammed into the corebook it's practically a given that you're going to want sourcebooks to fully-explore all the game's myriad aspects.
|I'd hesitate to call it "essential," but Scoundrels of Skullport adds so many more options to Lords of Waterdeep that it makes it a deeper, bigger game without becoming unwieldy.|