Is there a more detailed map out there than this one? (playing it on PS1): http://www.nosgoth.net/soulreaver/images/map.jpg

Can you do any dungeons/sub areas out of order? I'm at the second one and it seems like a mostly linear game.

Sorry that I don’t know much about the map.

There are some optional areas unlocked along the way. I haven’t played Defiance (my notebook is too old for it), but out of the other 3 3D titles, SR 1 seems to be the most (or maybe “only”?) non-linear one. For the main dungeons though, you’ll have to do them in order.

non-linear one

not so much. Even BO1 not true non-liner - just a lot of backtracking (mostly for secrets). SR1 have less secrets area (\not so big) and less backtracking.