KR,
Another place to learn about Alias is at
TV Tome where they have a general summary, then also break down each episode for all three seasons, and describe some of the "background" information (like the number 47). Otherwise, watching the seasons are another way to get into it, but thinking about how they ended Season 3, it seemed so different from the other seasons that I don't know how difficult it'll be to jump into Season 4.
Now that I've totally talked in random circles, I'm glad to see another person checking out Alias!