I played the game (without white march part 1) and i liked it.
Sadly, i've noticed that the best dungeon is raedric's hold in the whole game.
There are different ways to break into the castle and there are many ways/paths to move and reach raedric.
I think, it's a great example of good level design.
Maybe the temple of skaen is non-linear too.
Other dungeons are tendentially linear.
Honestly, I found Od Nua boring and repetiitive. There is nothing to do except to kill thousands of trash mobs.
I don't know if there are non-linear dungeons in white march, but i hope that in future (expansions or PoE2) there will be more open dungeons (like raedric's hold).
These are just my thoughts.
P.S. Sorry for my english