Factions have always been the best thing about TES because they've always dragged the content of the game out in unique and awesome ways. Not saying that isn't the case with Skyrim, but there's one thing I think they missed out on.
The plotline should always be there, but let it build into it. Almost every plotline is revealed within 2-3 quests of joining, and the College has it on the very first quest.
College of Winterhold - Plotline is revolved around the power of the Eye of Magnus, which you find in the first quest.
Dark Brotherhood - Plotline is revolved around the emperor's assassination, 3 major quests into the guild.
Thieve's Guild - Plotline is revolved around getting revenge on Mercer Frey, after 3 heist quests.
Companions - Plotline is revolved around the war with the Silver Hand and lyncothrapy, which are revealed in the 2nd (iirc) quest.
From there it's just progressing the plot, which makes them seem short and unrealistically rushed. I'm not saying I want useless filler quests, but extend the plot a little and have some quests early in the guild that don't mention the plot. Joining a faction and right away facing the major problems seems too coincidental.
