I don't know how people find this ending unpleasant, I mean, I went into this knowing the result but not the events that led to that result, and it even had a proper ending unlike almost every other series ever.
One of my criteria for a great series is something that has a proper conclusion, that alone is sometimes enough make a series great for me
One of the complaints I've seen was that the mio storyline wasn't as developed as the morikawa one, to that I'd say that the bulk of the story between eita and natsume was shown in the flashbacks, everything that happened from ep01 onwards was just the conclusion of the events that happened before eita moved out, at least that's what I think.
Haruto's entire story started with episode 1, and so it would seem to be more complete since everything was shown, but that's not really the case.
As with Komiya.. I think of it as just something Eita needs to get over if he's really serious with Natsume. "Here's this great gal that you have great chemistry with and is far more compatible to you than Natsume, are you sure you still want to pursue that girl you knew from years ago and once threatened to beat you up?"
Either way, Eita will end up with a nice girl no matter who he chooses, and since her entire story was shown, people are partial towards Komiya and I can understand how making her cry is just the worst thing ever, but throwing a pebble won't stop the flow of the river, so to speak.
as for that "unglamorous" ending, I think most people have just been spoiled by grand declarations of love that most other series do. At that point in the story they pretty much both know what the other was thinking, but they still had to say it, and they did.
All in all, I'm glad I picked this one up this season, it's the perfect story for the cold weather!