I liked Dungeon Siege better than Diablo, and Titan Quest was about equal for me.
Dungeon Siege II sucked major cause they changed the save-game thing, and I think that turned a ton of people off. You get used to how things work in the first game and then the add-on (Legends of Aranna) and you want them to continue to work that way.
Kinda like how Serious Sam TFE and TSE rocked, but Serious Sam II sucked totally.
What I liked most about Dungeon Siege from a gameplay perspective is that the thing is linear. It does not require you to do a ton of back-tracking or teleporting. In fact, one thing I did not like about the expansion (LOA) was that they introduced some teleporting. Hated that.
You cruise along in Dungeon Siege and manage your inventory and hold on to the key stuff and along the way you will find shops where you can sell your inventory. You don’t have to keep teleporting back to a central shop area or anything like that. They are just there along the way. I really liked that.