Most RPGs end up jammed into one of two broad categories:
1) Open-ended sandbox games which are usually a little thin on story and characters but make up for it with lots of freedom, choices, exploration, and moral quandaries. Oblivion and Morrowind and such.
2) Linear JRPG games like Final Fantasy, which have a fixed railroad plot but heaps of story and lots of (non-interactive) character development and dialog.
But developer BioWare always seems to be going for the best of both of these worlds. They make games with a large cast, a player-generated protagonist, a non-linear world, and lots of interactive dialog.
It's incredibly hard - perhaps even impossible - to make a game that's genuinely open and rich in story. But I always appreciate it when they try. I complain about their non-branching dialog trees and their odd mechanics, but the truth is that I love these games.
If you've played the BioWare games from the last decade, you may have noticed some really strong similarities between them. Some take place in the Star Wars universe, some in a high fantasy setting, some in a space-faring future, but the same elements, characters, themes, and plot devices appear again and again. Once you get to know these games, you can recognize what NPC archetype you're talking to within a minute or two of meeting them.
Think about how similar your companions are from game to game:
The Remorseless Killer
The product of a warrior culture, the Remorseless Killer is just doing his job. His grim, scorched-earth, genocidal, baby-killing job. Don't take it personally. Most of the time his awful deeds served the greater good. Or seemed to. He thinks. It's all sort of a blur now. Still, he can't help it so it's best not to dwell on the past anyway.
Unlike the Remorseless Killer, the Berzerker doesn't just go around killing people for some misguided cause. He does it for laughs! If you need someone to snap out a couple of witty one-liners while mowing down foes, the Berzerker is your man.
The innocent pilgrim is young, usually pretty, idealistic, and energetic. She's a free spirit and and isn't above the occasional theft. Or even frequent theft. The only time you'll have trouble with her is if you get into killing civilians and that sort of nasty business.
You see son, back in my day [insert plot exposition here].
There's nothing more handy in a big game with a new setting than an old-timer who can fill in the blanks for you while doing a lot of the "I'm too old for this" shtick.
Hey, we need to round out the cast but we don't want to have to write a lot of dialog or do any more voice acting. I know: Let's add someone who can't talk!