Reflecting back on some of the elements of the three games:
W1: Witcher 1 will always be special to me since it was a breath of fresh air at that time. Bioware was busy championing colour coded choices, and the less said about Bethesda the better. The morally ambiguous choices and the delayed consequences drew me in beyond my wildest expectations. The characterization was not the strongest in the series and the writing had odd turns of phrases on account of the translation, but the C&C style of the game carried it.
The individual quest design itself was not anything spectacular, resorting to constant A->B->A fetch quests and kill "x" number for contract quests, but the main quest structure was a revelation. I liked how quests received in the Prologue would not resolve until 40+ hours into the game. I loved the "thread" structure for the main quests where the quest designers split the main quest in each act into multiple threads that could weave in and out with one other, only to have all the threads converge at the culmination of the act.
The main quest itself never really came into the fore until the end of the game, instead content to play second-fiddle to the individual stories within each act, such as the Beast and the Village, Vizima confidential and Act 4. But the twist towards the end was what elevated the main quest for me -- instead of blatantly announcing the identity of the Grandmaster, the game instead elected to trust in the intelligence of the player and did so in a relatively understated manner (though it boggles my mind that some players couldn't piece together the identity).
The economy is also the best in the first game, since I was perenially running short of orens to purchase books, which lent credibility to the monster hunting contracts. I also prefer the style of music in the first game the most: most of the harmonies are quite simple, yet they evoked such strong feelings of melancholy.
The combat was simplistic to a fault and character progression was non-existent, with the ability to max out most of the useful skills by the game's end.
W2: The main draw for me was the politically charged story with personal stakes, in addition to the vastly improved writing. Characterization was also quite great, thanks especially to Broche and Letho. Dethmold was a character I loved to hate and Henselt's arrogance was well done. Even the quest journal being written in-character was a small change in the grand scheme of things, but added a lot to the characterization.
Complaints of the first game's repetitive quest design were heard, and effort was taken to make most of the side quests unique, in addition to retaining the "thread" structure for the main quests from the first game. Likewise, the character development system at least allowed for distinct builds this time around.
Music was a big disappointment, as barring a handful of tracks, the style of the music in the first game was shelved in lieu of more generic "epic-sounding" music. Combat became too twitch-heavy with ridiculous amounts of rolling around, random attack animations, and the alchemy system was gutted. I preferred the brain-dead combat of the first game to the frustrating combat in the sequel.
But my biggest issue with the second game is that it lacks a lot of the witchering that the first game had. It seemed CDPR ran out of time or money, and so only had time to include the critical paths of the main quest. The binary C&C choice that closed off half the content, though pretty brave for a mainstream ARPG, didn't help with feelings of a lack of content. The game desperately needed more quiet witchering moments like Act 4 in the first game to just let the world breathe a bit. Instead, the game sprints towards the finish line right from the interrogation sequence at the start.
W3: The game contains lots and lots of the witchering from W1 and combines that with the strong focus on characters and their stories that I liked in W2. Ciri's chosen one story was not my cup of tea at all, but that was balanced out by all the fun I had in dealing with Keira, Dijkstra, the Kaer Morhen Witchers, Triss and Yennefer's personal quests, and so on.
The biggest strength of the game is the framing of the quests; even the formulaic contract quests are framed with some sort of narrative that aids in reinforcing the setting. The meaty side quests are better than the main quests in a few recent releases, and the Bloody Baron and Ladies of the Wood quests is my favourite in recent memory. The "thread" structure of the main quests are alive and well here, and in addition, the game channels multiple Berengar-like quests from W1 at once, since quests involving Dijkstra, Radovid, the Crones, Philippa, etc., appear to meet a dead end, only to continue dozens of hours later depending on one's choices. Additionally, while the contract quests are framed compellingly, the auto-pilot investigation was a giant waste of potential. If those investigation sequences contained some actual player deduction with the the possibility of deducing the wrong conclusion, even the formulaic contract quests would have been a highlight.
The open world both succeeds and fails. It succeeds in telling compelling witchering stories through quests littered throughout the map. On the other hand, I cannot recommend the game solely to satisfy exploration lust. Too many questionable design decisions such as MMO-style quest level gating, MMO-style damage reduction buffs to high level enemies, loot downscaled to one's level, recipes generated inside chests randomly depending on one's level, and mostly useless non-witcher gear detract heavily from the exploration aspect. The UBI-style Points of Interest are also absolute garbage since they amount to nothing but tedious and monotonous content that do not play to the game's strengths of questing in the world. The game plays far better on turning those icons off, but they should not have been included in the first place, especially those "area liberation" activities that give more XP than several meaty side quests in the game.
The character system sees further improvements from the second game with the addition of alternative sign modes being the most interesting change. The limitation of 12 active skills was to my liking since I had to make conscious choices about the specifics of the build I wanted to play with. The combat is far more serviceable compared to the second, with sidestepping being far better than rolling around in the second game. There were encounters where I was completely in the zone and enjoyed the combat for what it was -- reading the monster attack animations and sidestepping them never got old, but this was counterbalanced by those encounters where half a dozen monsters attack at once, leading to the familiar incessant dodge/roll shenanigans or risk getting stunlocked to death. I played on the hardest difficulty and got used to the combat by around level 12, but I want the combat and encounter design to get reworked from the ground up for the next game. Boring predictable attack animations and encounters involving fewer but far more dangerous monsters is a combat overhaul I would like to see. It's got the strongest moment-to-moment gameplay in the series but there is ample scope for improvement.
I was skeptical about the alchemy system but it works well in practice, and it is my favorite in the series. Decoctions remind me of the lengthy potions of the first game, but allow for some interesting game-breaking combinations that are fun to fuck around with. The replenishing potions are probably my favorite change since I could focus less on picking flowers and more on witchering.
The music marks a great turnaround after the second game, and features my favorite battle tracks in the series, though I still prefer the slower pieces in the first game to those in W3. The composers must be commended for including remixes from W1 and W2 when one encounters characters from those games -- not enough games do this when it is such an easy way to evoke positive feelings from fans of earlier games in a series.
Overall, each of the games features flaws, some significant enough to be a dealbreaker to some, but I found the sum of the whole to be compelling enough to put up with the flaws of the constituent parts.
I'd rate the games as W3 > W1 > W2.