Easy question...Game of Thrones ! (both of them)
Given what a goldmine of lore the books (and HBO series) are and the HUGE fanbase this story already brings to the table, the RPG games could have been epic.
The first game is complete trash pile, the second one is only marginally better and still a waste of time and money and this is not only according to me but the critics, fans and every game review I've seen.
The battle mechanics are awkward and clumsy, the storyline is all over the place and it really is a shame when you look at similar games like The Witcher 2 and so many others that are just so much better, where the devs had so much less to work with than GoT did at the start.
Who knows ? Maybe they'll try it a third time and produce something good but I have my doubts at this point.