Do you ask just an opinion about this game (and previous ones of Larian)?
I can't compare them with The Witcher because I never played TW.
but my opinion about the Larian games is simple and for me, but sure not only me :
Very Great Fantastic Games ! delight

And: You won't regret it to play them for hours, days, months or even years ... biggrin

On 7th of february 2015 : I start a new adventure in the Divinity world of Original Sin,
it's a Fantastic Freaking Fabulous Funny ... it's my All Time Favorite One !