Fantasy usually bores me to death with its stereotypes, but I've been thinking about how much I enjoyed PS:T and Morrowind back in the days for feeling truly alien in their surroundings, cultures and creatures. There was a sense of wonder and discovery in those two settings that I haven't encountered in any other game since then, and I'd love to once again play something full of strangeness and/or mindfuck. Even just a fantasy setting that is not based on medieval Europe for a change would be nice, I guess.
Well, it's hard to find much stuff that would outrank PS:T and TES 3. In particular good, detailed worldbuilding and focus on alienness and alien cultures are rare.
From stuff mentioned in this thread (most of it not really related to fantasy):
Unreal has been mentioned - it's fun and immensely atmospheric (and I definitely recommend it as long as you can into FPS games and are into atmosphere pieces), but it's more of a refreshing bash of fantasy and soft sci-fi, than anything genuinely original.
If anything Half-Life 1 gets very alien later on (obviously not in a fantasy sense), but you only get observe, not really explore its alienness. It essentially made it for me, but it's still pretty much a standard FPS.
As for semi-original Sci-Fi fantasy bashes there is always Strife, which plays a bit like proto-Deus Ex in Doom engine.
Azrael's Tear is good, but i'd consider it something along the lines of... hmm... archeological thriller, with a dash of (underexploited) Lovecraftian undertones and some ancient conspiracy stuff, blended with Knight Templars and Holy Grail themes. Worth playing if only because this game is a genre unto its own - something you'd get out of integrating System Shock into conventional adventure (rather than the other way around), while forgoing traditional "gamey" FPS elements other than being able to shot stuff in first person (do note that "being able" doesn't imply it being a valid way to deal with problems throughout the majority of the game).
Might provide mindfucks, but I'm not sure about fantasy.
Anachronox is weird and awesome (and immensely lulzy, but surprisingly thought out sometimes) but only counts as fantasy if you consider all space operas to be it.
Dishonored is a decent suggestion, some neat fantasy elements, good atmosphere and interesting enough background.
Darksun is supposedly good, but I haven't played it, same with Albion and, sadly, Outcast.
As far as actual, conventionally fantasy games with nevertheless unconventional settings go, Legacy of Kain has been, strangely enough, omitted by this thread, despite being both good and very non-standard with rich enough background lore for it to matter.
So, any suggestions? I'd be fine with sci-fi that focuses on the weird and/or non-RPGs with a significant amount of exploration as well.[/QUOTE]
The Discworld games: well, it's Discworld! That should tell you all you need to know.
Yes - that it will fail to provide any mindfucks, if only because of how well known setting it is.