Eberron is a different setting, just like Greyhawk and the Forgotten Realms.
There are some differences with basic rules since it's a different world. All and all, it's not that big a change though.
There are some new playable races like the Warforged, golem race.
Alignment works a bit different as not everything that is evil in the FR is automatically evil in Ebberon.
I can't say to much about it though as I'm (since recently) also a FR man.
