I'd say both the original Divinity and the Dragon Knight Saga are worth playing.
However, both are also somewhat flawed gems.
Beyond Divinity has generally been received not so well, and I haven't played it, so I can't tell you anything about it.
DD1 and DKS are combat heavy real-time aRPGs where actual combat is a bit unbalanced and not always executed that well.
I think that both have lots of charm, plenty of Larian's typical humour and are typical examples of games that are more than the sum of their parts.
Divinity 1 has a large, open and fairly interactive world, plenty of quests but suffers a bit from some very imbalanced skills and quality declines towards the end (I think Larian said in an Interview that they never wanted to make the final area, but were forced by the publisher to put it in). Definitely has its fun moments.
In DKS you get to be a Dragon. World is semi-open (some parts are accessible only after certain quests, iirc), first 75% are typical combat-centric aRPG, last part (the original expansion Flames of Vengeance) is much more quest-heavy with more non-combat stuff. Again combat suffers from some balancing issues and was a bit too much relying on jumping around, imo. I think Larian admitted that they themselves weren't completely happy with it. Several original ideas whose execution was sometimes lacking a bit (e.g. mind-reading). Still I'd recommend it if you come across it at some acceptable (to you) price. Did I mention that you can transform into a dragon?
