If by balanced you mean following the rules in the three core rulebooks unless a new rule specific to the campaign supersedes an old rule, then yes it appears balanced. For instance, the DMG explains that an animal follower for a druid or ranger should come from the environment he's in. Eberron provides a list of animals by region.
However, Eberron adds action points, which means heroes in that world would be slightly more powerful than other heroes. However, since every hero has this ability it is balanced in Eberron (and in worlds using the Unearthed Arcana rule version I'd think).
Adepts have slightly more power in Eberron, getting the spells of one domain added to their spell list. However, every adept gets this boost so again it seems balanced within the world of Eberron (or any world that allows every adept this boost).
I haven't playtested Eberron yet, but I've been impressed by the editing so far. For instance, the artificer has starting gold listed, something the Complete books can't seem to bother with. Someone who wrote the book knows the core rules.
In my read-through opinion, appears well balanced and well thought out.