LOL It was a little annoying that the series doesn't give the closure of a kiss,but it was by no means unsatisfying. The characters stayed true to the very end, with kanda being hesitant and mashiro being the bolder one.
You don't care about aoyama,but I did. Personally I like how that wasn't resolved either. It makes it feel more relateable and less like a fairy tale ending(toradora). We don't always come out with our feeling in life because of circumstance. In aoyama's case, she didn't want to get in the way of kanda and mashiro.
Whereas that chick from toradora came out with a confession, an annoying one at that and there was no development on it afterwards.
The lack of kiss does, in a way, represent that there could be more to the series and even if there isn't, it gives a good end cliffhanger. However, the opposite would have done the same thing. A kiss reflects more of a relationship to come or a final conclusion to the series.
In the end, personally, it would have just been nice to see the kiss not from a plot point of view, but an emotional standpoint. Mashiro's emotions for Kanda were always cute, but what level would that go to if that final dive had been taken? The end of a season or end of the series, a finale like that would have been utterly amazing.
The show ended in a manner that reflects the maturity of the show's overall tone. Sure it would have been nice to "wrap" the ending up with ayomi giving up on kanda and a smooch from mashiro,but that would be the way out.With this the world continues to move forward, regardless of what happens to sakurasou's gang.