The problem with alot of RPG's is they get dull and boreing after awhile. I have yet to see a true RPG that does not get dull after about a month of play. You need a game that is open ended but yet gives you direction of what to do next.
If you can stomach ASCII(letter-based) graphics, you'll get just what you're asking from 'roguelike' games.
They're not interactive fiction games, no 'take sword, kill goblin' kind of commands. It's more like playing old Ultima's or Wasteland, but with a different world every time you begin.
I'd recommend ADOM(www.adom.de
) to start with, but there are many worthy ones.
If you'll get put off by the graphics and interface of those games, keep in mind that in roguelikes you can...
...not discover half of the game's secrets in a year of playing, yet stil be suprised in every game.
...get polymorphed into monsters, drugged, die of hunger, kill a goblin and eat it.
...make iron rations out of the goblin
...make the goblin your undead servant
...find artifacts that can destroy a whole race of monsters at once
...cut down a tree and use it as an improvised super-heavy club
...tame medusa, make her turn somebody into stone and use him as an improvised super-heavy club
And those games are also very hard:)