as for the filler, ergo proxy was basically one filler after another filler, after another filler, except for the beginning eps and the end. But it's somehow tied together to make an interesting and engaging story.
Every ep I kept expecting shit to go down, for main char to just fuck shit up, but it never really happens, but (although i really like action anime) this didn't really bother me; rather it made me like it even more.
Ergo Proxy is one of my favs, and probably once a week or so I'll have that stupidly awesome little girl stuck in my head saying 'usagi' while prancing around.
That said, ergo is an awesome anishit and one of the best out there.