A good number of these are frustrating in that they go through the formation of a relationship, but stop at a point where everything's still just hanging in the air, not yet made into something definite and substantive, the lead-up to romance but not the romance itself.
Well, I suppose that in and of itself is fine, except the catharsis in them is generally also weak; so it feels like reading a bunch of first chapters that end on good moments of repose but don't really wrap everything up emotionally.