For their latest WRPG-focused weekly column, Joystiq's Rowan Kaiser writes about the reasons why he thinks Fallout is the first genuinely modern RPG. That's a bit of a controversial statement, so here's a snip on why he feels that way:
Because the game was a lone character's story, the choices you made in developing that character mattered more. You couldn't build a jack-of-all-trades. You had to focus on a few key stats and skills, and that meant ignoring others. When I've played, I've usually made a fast-shooting, fast-talking scientist, but there's nothing stopping you from making a stealthy, blade-wielding ninja, or, famously, from making a character who can finish the game without ever entering combat mode. But this comes at a cost. You won't see parts of the game if you don't have high lockpicking, or high speech, high luck, or badass combat skills. Making one choice eliminates others.
The game is built for this. Cain described how for every major quest, the team had three different options: combat, stealth, or speech. There was variance within these: the natural variance of different modes of combat, stealing/sneaking/mechanical skills, or barter/charm. Cain said that side quests didn't necessarily have all three, but many did, with almost all including at least two options. You could play how you wanted within that system.
This, more than any aspect of Fallout, keeps it special. Virtually every one of its successors has added stronger companion or party systems. In Knights Of The Old Republic, your character may not be able to open a locked chest or door, but because they can't you'll probably have brought Mission Vao along with you to do so. Only Deus Ex has really matched the first Fallout in terms of individual, statistical development and choice.