Maybe you should start with the 8 resp. 6 party members, number/type of stats and character development (how classes grow), control scheme, ...
Look, frankly, Dungeon Siege doesn't even HAVE a 'feel'. DS1 and DS2 were quite different, and DS3 is different again (for the better, based on what little I've played so far).
But what I really wanted to point out is that, while I agree with Pidesco, he is a moderator, not an Obsidian employee. Please don't misinterpret his comments as coming from Obsidian.
Quite different... !???
I could imagine that many DS1/DS2 gamers won't share this point of view - specially when facing this DS3.