Jay at Tales of the Rampant Coyote nears the end of his romp through Wizardry 8 (so spoiler-heavy) and draws some design lessons from the game.
If I recall correctly, Richard "Lord British" Garriott once said that he'd make sure there was always at least one good way to achieve any goal in the Ultima series, but that he wouldn't go out of his way to prevent other approaches from working. If the players figured out a clever alternative, he was fine with that.
While a few more recent games have seemed to at least give nods to this idea (The Elder Scrolls IV: Oblivion and Vampire the Masquerade: Bloodlines come to mind, and I suspect Fallout 3 falls into this category as well), it is too often missing in many modern RPGs. While I've not played it yet, Shamus Young has recently excoriated Fable 2's plot for gross negligence in this reguard, forcing the player into some really bizarre, idiotic, needlessly complicated and punishing paths to accomplish what appears to be otherwise straightforward goals.
And even Oblivion seemed ... well, oblivious... to the fact that I'd accomplished one Thieves' Guild quest without actually killing anyone as I was assumed to have done. Those blind monks never even knew I was there, dang it!
Part of the problem, I suspect, is the script-based approach to handling "quests" or missions. I'm struggling with the same issues in Frayed Knights. To make things interesting, the entire sub-story and path to accomplish the quest is scripted out in advance, and any alternative approaches have to be similarly designed, tested, debugged, re-written, polished, and perfected.
But is this really necessary? Couldn't the Lord British approach still be applied to modern games? So you've got the glittery orb quest item stuck in some room. Is it really necessary to dictate how the player obtains the orb? Must all events and approaches be deliberately scripted into the game, or is it possible to set up a more generic event system and let things proceed more as a simulation? Would it be just as exciting? Just as interesting?