1. Witcher: best soundtrack hands down, mainstory was unpredictable with plot twist, perfect atmosphere, more attack animations then Witcher 3? What happend there CDPR? little to no hand-holding unlike 3, animations for drinking potions, applying oil, sharpening weapons, meditation only near camp fire, no ciri etc. I could go on and on. Great game back then and still the best Witcher game.
2. Hearts of Stone: best soundtrack after Witcher 1, amazing Antagonist, pacing was very good, challenging fights again and nice bossfights, exploration/loot was improved from Witcher 3 maingame, again no ciri (just saying this to piss off ciri fans)
3. Witcher 3: voice acting was top notch, great facial expressions, best combat out of the 3, brought back some atmosphere from Witcher 1, seeing eskel, lambert and vesemir again, so many interesting characters, best sidequests in an Open World game to date (though Witcher senses are overused and make the quests basically auto-pilot, Geralt tells you everything, as if the gps was not enough), progression system was unrewarding, sadly the weakest mainstory, shallow main villians , wtf happend with radovid? very predictable, no big twist and of course Ciri.. pacing is bad probably because of the Open World. So if I leave the expansion out its the second best Witcher game.
4, Witcher 2: very cool antagonist, begins directly after Witcher 1 ended as far as I remember, Foltest is a bro, amazing graphics back then, better mainstory then 3, politics, two different act 2 very bold, more mature themes then 1 and 3, weakest combat system even though Witcher 1 combat was simple it was a lot more fun, QTEs, QTE Fistfights, weakest minigames and the amazing atmosphere from Witcher 1 was missing.
All of them have there strengths and weaknesses no Witcher game outright sucks or is bad, but 2 is my personal weakest out of them, despite having a better mainstory then 3.