Whatever the failures of the Witcher 3, you can at least play the whole game in one go versus getting locked out of a third.
The issue I must put an accent on is the lack of logical continuity - Ciri by the books actually after the whole thing with Gerlat dying, married a veteran of the Brena War (the one she met in Vizima when he was 12) and neither became queen, neither a witcher in her childhood dreams and neither disappeared
Witcher 2 succeeded moderately in taking care of the Witcher 1 heritage of choices, though many were lost even there.
Siegfried in Act 3.
On everything else - read the books.