I maintain that if a game lasts less than 100 hours, you weren't playing it properly. :p
That excludes arcade games and most RTS games. They should end quickly and be replayed in a different way.
As for RPGs though, a game that lasts less then 50 hours is not really worth my time. I have been playing Morrowind and have yet to do a tenth of it after 68 hours.
That's not necessarily true, because you can't "Beat Warcraft 3". The game doesn't end when you win a single match any more than Final Fantasy 7 ends when you win a single battle or complete a single branch of the plotline. Thus, the game can easily be said to contain more than 100 hours of gameplay -- and if you aren't spending that much time playing it, it could be argued that you are playing it "wrong", though I wouldn't necessarily say that to most casual gamers. :-)
But only 14 hours? I'm wondering if I really should bother with the rental.