In fact - there is NO online gameplay and NO customisable rockers...
Still brilliant fun! For those looking for something to fill the void while GH:IV comes out, this should do it.
Best part for me is the drums. Rock Band is the first game to bring the drum kit out (although to be honest, Guitar Hero 4's looks better), so i'm spending my time kicking out the jams.
The guitar is slightly different - you can throw on custom effects like chorus or echo, and you can play higher up the neck which really only serves to look like you're soloing proper. I found the guitar buttons way more sensetive than guitar hero's, but in time i'm bound to get used to it.
I haven't played it too much with other people but i've found rocking out on the drums is so much fun I don't particularly care!!