I was always buying it(I think), keeping it is whole other issue.
If I feel it'll collect dust like Morrowind did after 10 hours, its going on ebay. If its too vast, I wont be able to keep focused on it and I'll end up playing my other games instead. I may however just go thru the main quest and sell it afterwards if its truly only 25 or so hours. The 200+ hours isnt my thing, hence why I liked Fable, nice and short and if it was any longer of an adventure, I wouldnt have cared for it.
*If* I think it looks like ass and it just so happens to have jaggies that are unbearable, the main quest wont see more than an hour, its either being exchanged at EB for FarCry or Tomb Raider, or on ebay it shall go. I am by no means a fan of RPGs. Fable is the only one I ever bought and finished and liked. The rest were either 2 ugly and boring, or 2 long(morrowind).
It could turn out to be one of my all time favorites as well. I stopped speculating long ago about this game, not worth the troubles honestly. There are games out there that I KNOW will blow me away, those are the ones I care about, I bought one of those last Wednesday
Ghosts! Mount up!
Oh and let me add that if the visuals please me, and I already know the in game music rocks(been listening to soundtrack all day), that could be enough to keep me interested for a while, long enough to finish the main quest anyways

Don't worry, it took the OXM team 40+ hours to beat the game.
But they did say that there's plenty of side quests to keep you gaming for up 200+ hours.
I'm with you, I totally loved Fable (I'm waiting for Fable 2).
It was long enough for me....
As for Morrowind, I never really got into it because I didn't find the time.
But I'll be sure to make time for Oblivion. 40+ isn't too bad, I mean I played through both Star Wars KOTOR games easily. And if Oblivion is just that damn good and addicting, who knows maybe I'll play through the 200 hours