Gothic 2 with addon "Night of Raven".
If you know Russian, you can also get free fan-made addon "The Returning". But even original version is superb.
Also, there are free mods with separate adventures. Most of them are on German\Polish\Russian, but also a few English ones.
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Vampire the Masquerede: Bloodlines is also one of my favorite RPGs. Also has fan made mods that make the game even better.
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As for Adventures - go for King's Quest series.