The fact that it's not a completely hopeless crush doesn't really change the fact that it fits right into Nakatani's favourite theme, that being quiet one-sided longing. It's not tragic, but it's still bittersweet; it's a thirst that wants to be quenched, but at the same time, there is something oddly pleasant about having a little secret crush on someone and being able to privately admire them from the sidelines.
Still, I'm not going to blame people for being disappointed with a story where the focus is 100% on the tension of longing, with no intent to release it. For plenty of people, the idea of leaving a story with an unresolved tension that will, by all signs, continue to build with no sure sign of relief is itself a mark of a sad ending, and their overall experience of the story will be coloured by that impression. I don't think that's an unreasonable reading to take from it, either.