I played (and modded) DS 1 and 2 pretty extensively, including a couple of Total Conversions. It was reallt two games in one. The Single-player game was standard linear map, with enemies that progressed from one end to the other, and the multi-player game used the same mechanics in an open-world map, with more random enemies that you were warned away from if you were low-level.
ghastley.org/DS/ has a bunch of poorly-organised stuff of mine, including things you can download, tutorials on modding, etc.
Dungeon Siege III shares only the name. GPG sold out, and the new owners made a no-mods mess of a sequel.
Beware of broken links on my site. A lot of other sites have disappeared, and I switched my server from MS IIS to Apache on Linux, so the case-sensitivity differences broke some, too.