Hands down, Planescape: Torment is one of the most influential, unique and really, best RPG titles ever created. As someone who is both old enough and fortunate enough to have played when it came out, I can attest to the same fact.
Even today, after so many years, it is an essential role-playing game for anyone who likes this genre. From the incredible story to the rich gameplay and numerous mechanics, to the fact that it actually provides a resonating overall experience, this game has it all. Most of all, it has that super-weird atmosphere that has never been seen before or after it (so far, at least).
The title has been ported to Android and managed to keep all of its glory - even though many note that it is best played on a tablet device (thanks to the otherwise tiny text on smartphone screens). If you haven't tried it, now is the perfect chance - Planescape: Torment: Enhanced Edition is on a 40 percent discount on Google Play!