All the games that I would put in my top 10-20 list I love mostly for the story. Although I also tend to enjoy the gameplay of everyone of those games, it is the story I walk away from feeling touched.
I don't really play Heavy Rain for the gameplay for example, Dear Esther and Portal is another example. Although I love all three of those games. Portal has good gameplay yes, but I haven't gone back to it 10 times for the gameplay.
ALTHOUGH, on the other hand, I really love these rogue-like type games like, Dungeons of Dredmor, FTL, XCOM and Terraria. Those games have little to no story and I don't play ANY of them for the story, I just LOVE the gameplay.
Gosh now that I think about it maybe I do fit somewhere in between. Most RPG's I love tend to be a great mixture of story and gameplay. I would say I value story much more than gameplay, but I do like enjoyable gameplay as well.
Dragon Age is a good example for me of a really great game that I enjoy the story and gameplay about the same, in an RPG like that, I don't think I would play unless I enjoyed the story AND the gameplay, although I feel the story is more important.
Fallout 3/Skyrim is another game for me that I love both story and gameplay about the same. Living in a high detailed strange world with so much to explore and a high focus on aesthetics and atmosphere.
All in all, it is the story and passion that sticks with me and that I value in the end. Fighting the colossi in SOTC is a great experience, but that isn't why it is in my top 5 favorite games.