I've yet to complete the other factions quest lines but I was so disappointed in the Brotherhood of Steel Quest line! I didn't expect for it to have as much of an impact / role as they did in Fallout 3, but I expected a bit more! I was hoping that I would be able to feel like I really am part of the Brotherhood of Steel, but this is not so! Instead, I feel like just an errand boy with benefits!
...That's exactly what you are to them.
- More Quests
- Random Quests ( you walk in and occasionally receive a quest to kill certain creatures, or to help out a team of BOS Paladins on their battles )
The Brotherhood questline was already incredibly long. Any more and they'd probably end up being a major faction rather than a minor one.
Ability to pull out squads of Brotherhood of Steel Paladins to aid in your adventures ( With limits of course ) You can actually do that with the NCR path, sorta.

Ability to achieve a higher rank than that of Paladin if you stick with them There
is no higher rank than Paladin. Except head/senior paladin, which is only granted based on seniority.
Now, as I've said I haven't completed the other factions quest lines but I doubt they actually make you FEEL like you're one of them. The brotherhood of steel instead make you feel like an errand boy with benefits. Although, if you know of a faction that actually gives a sense of belonging then let me know!
Yes Man's faction.
As it stands, the BoS in the Mojave doesn't do much of anything except hide in their bunker, which allows people who've only played FO3 to think that they're a bunch of "good guys".
Well, the first introduction to them involves them slapping an exploding dog collar on you, so it's hard to consider them good. Unless you go with Veronica, in which case she talks a lot about how the Brotherhood doesn't believe in helping people.