Card tried to put too much in that book. Before it was released, people were lead to believe that the main plot of the book would be what would happen after Andrew reaches the first colony world, because what happens on that world pretty much drives the plot of Speaker For the Dead. Also, Card himself said that what happens on the next world that Andy and Val go to was going to be the main focus of the book, and it even says so on the (rather hilarious) book jacket.
Instead, the book deals mainly with what happens before Andy and Val even reach the first world where Andy's governor. So there's a lot of build-up with characters who are interesting in the beginning of that book who get no closure because they were introduced in the beginning of the book (with a full given history and everything), became damn near main characters because of how much they did, and yet just kind of disappeared in the middle of the book because Card realised that he actually had another plot to include in one book.
So both parts of the plot (what happens before the first colony world on the spaceship and the colony worlds) are rushed to fit into one book. So the main part of EiE (what Andy finds on the first colony world that drives the rest of the series, in a way) is rushed and falls flat, because Card focused more on getting to that point, and also had another plot that gave some closure to the Shadow series to include.
Really, the entire book could have been split into two separate books, giving Card time to focus on each part and giving a satisfying ending.
Instead, the actual ending of EiE is short. Big emotional scenes are given nothing, and entire changes of characterization (a character realizing that his entire life was full of lies) is simply brushed away and given no thought because it was close to the end of the book, and Card probably ran out of pages. Or was tired. (The man plays a lot of video games and watches a lot of television, y'know.) It's just pushed aside and given nothing more.
So really, the entire book is missing a lot of what was in Card's older works.
I would say more, but then that would just be getting into spoilers, and also making me want to write fanfiction. holy crap, protectorshipping <3<3<3