Like most other things genres are somewhat blurry. In terms of the biggest classics that have aged well from each of gog's genre bestseller pages I'd say:

Action - Beyond Good and Evil, Thief/Thief 2 and Chronicles of Riddick (although most would call the latter a shooter).
Adventure - Monkey Island, Longest Journey, Broken Sword. Maybe Gabriel Knight and Grim Fandango but they're still on my to do list. Tex Murphy is enjoyable but you have to persevere with the controls for the early ones.
Indie - Not a genre.
Sports - GoG doesn't have any of the big games.
RPG - Baldurs Gate II, Deus Ex, System Shock 2 maybe the original Witcher or Planescape Torment.
Shooter - S.T.A.L.K.E.R - Shadow of Chernobyl. Most big shooters are too new to be on gog or too multiplayer focused to be something you can come to later.
Simulation - Sim City 3000/4, Rollercoaster Tycoon.
Strategy - Gog is missing the big sellers like C&C, Starcraft, Age of Empires, Warcraft etc. but there are a lot of very good lesser selling options like Galactic Civilisations, Startopia, Total Annihilation, Men of War & Space Rangers. I'm also a fan of Europa Universalis III/Crusader Kings but they are less mainstream.

I agree that saying what one liked and disliked in a game is the best form of critique, but ultimately it relates to only one game, my recommendation of Witcher 1 is really about stqrting with something cross-genre. I don't consider TW1 a pure rpg, I think it has a very rich gameplay (actiony-adventury with very good story telling and lore, which is sadly not that common in RPGs in general).
Finding what on's preferences are is not the same as finding what games you'd more likely prefer. In my experience for instance, I absolutely love Fallout 1, Morrowind, Super Metroid and Witcher 1, but my favourite genre is Tactical games with (or without) a bit of strategy like Fallout: tactics, FF Tactics, JA .... and Sacrifice.

Well, what I'm saying is that I don't believe there actually is such a thing as a "pure RPG". And personally I found the action in the Witcher dull, not that much superior to the subpar combat in Torment, and I thought the story telling, lore and adventure elements much stronger and more captivating in the latter. Not that I can't see why TW1 would be somewhat more representative of the genre, just saying it's still not representative enough to stop there and judge the genre on that basis. Much less even to treat it as a showcase for several genres in one.

To summarize, I agree with you that Torment can't give a good representation of the genre, I just disagree that TW1 would be that much better in this regard.

Thank you so much for the warm welcome :)
You are not easily deceived, I have played video games before, but I haven't played many since... The early-mid 2000s when I was around 9 years old. I played a bunch of games, and even a few console games here and there over the years, but I mostly enjoyed watching friends talk and play games rather than playing them by myself. So yeah, since 2003ish or so, I haven't played too much. As many images as I remember seeing from all sorts of games, I was too young to really understand what was going on (I was/am a stupid kid).

So... In a way I am still new to gaming, if that makes any sense :)
Again, thanks for all the recommendations and the kind welcome!