Actually, you can get into the sealed room by tossing a teleporter stone through either of the gates.
Beyond Divinity is similar to Divine Divinity, though if you expect them to be very close you might be disappointed. There is a
demo if you want to check it out (there were some changes and additions made after the demo was released). BD is divided into 4 acts, so it is less open than DD. The first act is relatively linear and mostly hack and slash, but later acts have more freedom of exploration and variety of quests. The skill system is much more flexible (some think too flexible is a couple cases), with books or teachers to make skills available, rather than character level requirements. Combat is similar, though controlling 2 (or more) characters can add a bit of complexity, depending on the situation.