I think OA would have worked better if they made it longer, staged, and almost the first thing you do coming out of the vault. It would better explain how some Vault Boy with a BB gun could become the savior of DC.
1 - Coming out of the vault, you are met by an Outcast Patrol. They see you have a pip boy and "escort" you to their base.
2 - You do some training sims, starting with fairly easy, but working your way up to tough.
3 - You finish the DLC with the standard OA missions.
4 - You're dumped outside the base, but with some goodies - a few weapons, some ammo, some decent armor, and most importantly, the skills needed to become savior of the Capitol Wasteland.
5 - Megaton is the only marked spot on your pip boy map, so you head back to it and continue FO3's main quest... or not. You now have skills and some stuff, so you can now do whatever you want.
THAT would have been a much better OA.