Yeah, it's a weird pick. I really only like it because Chain of Memories was my favourite KH game and I associate the song entirely with my memories of it. It's not a particularly interesting or impressive song otherwise.
I feel the same way, though. The entire Chrono Cross soundtrack is like that for me. I've never played the game but its soundtrack is one of my absolute favourites. It's to the point where I'm almost scared to play it because I feel like if I do, I'll be disappointed that the songs don't match the kinds of scenes I've expected them to in my head all these years...
I think that a good videogame song should be able to get you in the mood even if you haven't played the game and this one manages to! The castle one you said, on the other hand, doesn't. That's how I evaluate songs XD
:> It's an amazingly epic song when the first time you hear it is when you get to an extra boss you've never seen before during your level 1 run AND manage to beat it too and on your birthday. I always feel like I like the song just for the memory I associate with it but it's nice to hear other people like it too! xD