It's been so long since I read it and I sold my manga, so I don't have it to look up, but I don't remember being dissatisfied with the ending (other than not wanting it to end at all because it was a favorite). But I didn't have any attachment to Hikaru/Akira (either as a pairing or platonic) and like open-ended stuff, regardless of whether it's Japanese or western, so... ^_^;;

I think the only manga I've been really disappointed with was Shaman King, in which the author wrote himself into a corner and then just sort of quit. >_<