Yes, Beyond Divinity is worth getting, especially (in the case of the Divinity Anthology) if you also want Divinity 2 Developer's Cut.
It is kind of Larian's red headed stepchild, though, with a fair bit of criticism when it was first released, though IMNSHO mostly invalid (ie easily avoidable issues) or exaggerated, or merely a reaction to not being more of Divine Divinity.
Some of the voice acting is pretty bad, but most of that is concentrated on the first level; the DK's voice gets better as the game progresses, and he talks less.
Some of the skill design was more complicated than it needed to be, especially with the different resistances, though you can easily avoid that by sticking to weapons that do conventional damage.
The music, writing, atmosphere, etc, is similar to DD.
There are 2 main characters that you control (most of the time you can have them both selected, and direct them to move or attack as one). Combat is a little more tactical than DD, with approach, positioning and target selection more of a factor for tough fights.
Some of the new things BD tried worked well, such as the summoning dolls and stat system (it allowed a great deal of flexibility in creating viable character builds; in DD all warriors pretty much ended up with the same stats), etc. The battlefields are great for handy access to merchants (the randomly generated dungeons are optional).
With the characters and equipment being in 3D, there is a lot more variety in equipment in BD, which is reflected on your characters (in DD all large shields looked the same when equipped, etc).
BD is a little more linear than DD, being divided into 4 acts (act 1 opens up towards the end, and acts 2 and 3 have quite a bit of freedom in where you can go, with more variety of environments), though that fits with the plot of the game.
