It would certainly be nice to have a file checker. While my internet's decently fast, redownloading a game upwards of 30GB isn't as friendly to my ISP's newfangled bandwidth limits.

SE could even probably take a note from some other games and do the whole file stream thing for newer players too. No reason to prevent a person from doing 2.0 content if they don't even have a character progressed far enough to enter 3.0 and 4.0 maps. (So let people login with a partial install if they can access those areas!)