There certainly is no comparing the Baldur's Gate series with Dungeon Siege. They are two totally different games in most aspects, other than they take place in a fantasy setting. I personally don't care much for the action RPGs, but as far as they go, Dungeon Siege is a pretty good game. I've been playing it for a few days now, and other than the hack and slash, it's actually kind of fun. The graphics are wonderful, and the interface is intuitive and easy to use. I also like the soundtrack, especially when you're traveling through the Ice Caverns - the drums are pretty cool.
I don't even begin to think BG when I play it. I played the original Diablo when it was first released, and so I liken it more to that. I didn't really like Diablo either, but then it's simply a matter of what one likes and doesn't like. Me, I'm a D&D fan. That's why I'm not enamored with DS, but I recognize a good game when I see one. DS is pretty decent.