I'll be able to comment more on this after I play my marathon.
The only ones I've beaten are I and IV. Back then I thought the stories were amazing, but then again I and IV are the among the first two RPGs I've played.
7, 8, and 10 I thought were interesting but I think I just got tired of them. Then again I played them in my early to mid teens and probably just didn't have the patience for RPGs. In fact I rented 10 twice, didn't beat it, then didn't play RPGs again until Oblivion a few years ago.