@alyx
You cannot join all factions.
That is GREAT, and the thing I hate about Skyrim/Oblivion.
@LukeAlmighty
It's obvious that the reasons they made it so you can join every faction in one playthrough is that they don't want people to miss out just because they're not willing to start up multiple characters.
But this only highlights the true flaw of modern TES: the games aren't sooo good that they make players want to start up a new character as soon as they finish the first.
@LukeAlmighty
You're more like a god incarnate. A sort of Jesus. Sure you can do the equivalent of miracles, but you're not exactly immune to being killed by unbelievers.