The third is an absolute must play. Don't let your experience in the first two games influence that. Even my brother played and completed Witcher 3 after I insisted. He's the sort of guy who never ever plays RPGs and just plays Call of Duty every night on his PS4.
I've played a lot of RPGs, including the main ones like Dragon Age, Skyrim, Diablo, Zelda etc. and am huge fan of Dragon Age in particular, but no RPG even comes close to The Witcher 3 in terms of dialogue and questing, which make up 70% of these games. The small and inconsequential quests that are such a bore in pretty much ever other series, are downright fascinating in The Witcher 3.