RPGs and strategy games are the main games I play.
I personally consider the Witcher games my favourite games ever. The stories are indeed darker than your average RPG, and are full of moral ambiguity; you can support different sides in conflicts in different playthroughs without either choice necessarily appearing either “correct” or “evil”, for example. They’re also very good at characterization, I feel; IMO the Witcher 2 has the best (as in well-developed, 3-dimensional, and realistic) characters of any video game. The games also freely deal with issues of drugs, sex, racism, and fanaticism, as well as violence (violence and oppression normally being the only visible evils in most games). Like Planescape: Torment the games are best if you take the time to get immersed in the game’s world (talk to characters, read books and descriptions in-game, even consider reading some of the stories by Andrzej Sapkowski that the games are based on).
The complaints I’ve heard about the Witcher games are mostly based on opinions about the gameplay – personally I have no complaints at all. There is a lot of combat, but that’s true of all the games you mentioned as well. If you pick the easiest difficulty levels it’ll never get in the way, if you just want to get into the story. Play them in order if you get them - it makes more sense that way. 1 is also simpler to get into, longer, and IMO, easier.
As for other games: the Dragon Age games are very good. 1 is more open and has an epic story spanning a whole country; 2 is much more limited and restrictive, following a set character’s life in a city and its environs. 2 is generally considered a worse game, even poor by comparison, but I still enjoy it.
For older games, there’s Knights of the Old Republic, 1 and 2, in the Star Wars universe 1000 years before the films. Even if you hate Star Wars, they’re solid games, especially 1 – and better than the film prequels. 2 is buggy and unfinished (literally – the ending as-is provides no closure, and some aspects of it make no sense), but the story has some great moments and ideas along the way, IMO. But if you only want to try it out, definitely get the first.
There are some shooter-RPG hybrids like Mass Effect and Alpha Protocol. The Mass Effect games are great, and on sale on Steam today. If you hate shooter games, you might not enjoy them – but if you’re open to the idea, they’re actually really good and tell an interesting story in an interesting world. I was actually skeptical at first, picked the first game up in a Steam sale, and now I’m a fan. 1 has a solid main story; 2’s plot makes little sense when you think about it, but has very streamlined (in a good way) gameplay and great characters IMO. Alpha Protocol is a buggy mess hiding a gem – good design and writing screwed over by lousy production, apparently. If you can put up with buggy, imbalanced, and sometimes frustrating gameplay, there’s an interesting experience underneath – particularly as it’s one of the only espionage-themed games I know. In short, many people consider the game crap, but I personally really enjoyed it.
Vampire the Masquerade: Bloodlines, mentioned above, is another game I really enjoyed, but it can also be really frustrating. Buggy – though mostly fixed in community patches – and full of action which isn’t necessarily always fun. I consider it more an action game than a “real” RPG, but enjoyable.
There’s also Divinity II: The Dragon Knight Saga, also on sale on Steam today. I have it but haven’t played more than a few minutes, so I can’t comment on it.