In fact they seemed to have returned younger, like debut album younger. Bye Bye Bayou is not an entirely new composition by any means, it's a cover of an Alan Vega (Suicide) song from 1981.
A seven minute rolling yet relaxed jam that doesn't go anywhere fast but doesn't really care about that fact, it's down with that and doesn't care if you have a problem with it.
It doesn't grab you instantly like some past efforts have, but Bye Bye Bayou isn't set to appear on the new album (which is due out March 2010) so how much truck you wish to invest in it is up to you.
It's just nice to have them back.
mp3---> LCD Soundsystem - Bye Bye Bayou (via box.net)