The ending is just excellent. It refrains from rushing their relationship, stays consistent with the characters, while at the same time providing a clear view of what will inevitably happen. Of course they're going to end up together, but having them suddenly confessing would've been out of character, and while I can't deny that I just want them to get together already, the ending we actually got is ultimately far more poignant and fitting to the show. The way their relationship develops and unfolds might just be the best romance I've seen thus far in anime. It's natural, sweet and earnest. They really make for a great couple. Their "game" in episode 20 is just adorable.
Most romance anime just end by the two characters dating. Hyouka ends by making it clear to the viewer that the love the two leads have for one another does not stop at dating, but extends to the idea of marriage. It doesn't need to do anything more than that.
But god dammit, just kiss already