2) A related, and perhaps more important, question would be: do you find IF enjoyable when you can greatly affect the journey but you have only limited control over the destination?
I enjoyed Choice of the Deathless, which allows for some variation before you get to the big confrontation, but…
[somewhat spoilery ahead]
…I did feel a little frustrated/steamrolled into the exact same final confrontation every time. The story begins at that fight and loops back into it at the end, but I might have enjoyed it more if it weren’t predetermined that you always fight the same person. If the Big Bad and the Big Bad Plot revealed at the end were different, depending on whether you eliminated any other threats along the way. After a certain point–albeit close to the ending–I felt powerless and felt that my choices (and my time) were wasted, if no matter how I chose to fight, however much I picked up a clue beforehand that something was going wrong, I’d always end up in the same climactic moment. In other words, the game went on too long after the point where the climactic moment was inevitable, asking the player to make battle-related choices that were completely irrelevant. That worked OK on the first playthrough, but made me impatient and irritated on subsequent ones.
That said, it’s a smart, smart game, very replayable, and the tools you have for that final battle differ depending on how you play the whole game. The endgame–whether you survive, who is there for you afterward–all those depend on what you chose beforehand. If there were a sequel, there’d only be a few variables the author would need to carry over into the next game, along of course with any relevant stats. The MC could go off into a new adventure, because (in my take) it’s more about how the MC is different at the end of the game, not how the entire world is completely different (as if, for example, in one ending the world is reduced to rubble, but in another ending it’s a paradise).
If Book 1 always ends with the Evil Empire being destroyed, but also with the choice of the hero going off to live on the Moon or choosing to stay behind on Earth, Book 2 could concoct a reason for everyone to have to go have an adventure on the Moon and continue from there. One MC might have better Moon-related stats than the other one who stayed on Earth.
I hope all my babbling explains what I think makes for a successful game even with a predetermined destination.