Hmm I heard before release you could join as many factions as you wanted (as long as no conflicts occured, I guess?)
So I'm interested in listening what the Railroad has to say, but haven't bumped into them yet. So I currently think they are people who have fetishes for robots.
I mean, I don't see the point of that faction just by hearing a tape and reading a note from them. Probably there's a whole lot more to it, though.
I joined the Brotherhood as initiate and I'm doing their stuff. As you can hear in probably the first holotape about them, you'll hear that:
The leadership is "misguided". They are too violent, and probably lost much of their vision.
As my character is thinking highly of himself because he's a "natural leader", he wants to fix that.
I also joined the Minutemen. I think they are a basic foundation for the future of the Commonwealth.
But they seem overly stupid (Hey, let's save the world by walking around looking dumb with some flashy guns and protect people! We don't know what tactics or strategy are, though, but that's pre-war stuff!). Seem like it needs a dose of a Lone Survivor to get them on the right track.
Still don't know a whole lot about the factions though, and BoS/Minutemen is really the ones I have contact with.
I didn't do many quests yet, as I always go around exploring and building.
And by the way, the first time I saw someone walking in a T-60 was pretty awesome. It looks great!