To say JA "got it wrong", as others alluded to it, is not quite appropriate: they are her characters in her story, so we can say we would prefer an alternate pairing but it's only our own interpretation of JA's characters and situations, influenced by our personal and cultural background. The author is the final authority on how her characters are to find happiness.
I can interpret Col. Brandon's attraction to Marianne without it being morbid: he is attracted to a certain type of woman and just not attracted to a different type (embodied in Elinor), even if he likes and respects her.
As for Edward and Elinor, their whole romance is underdeveloped, to use Suzanne's approach: we get to know Elinor's feelings and how she deals with them, but not much of Edward's side of the relationship, except for his final explanations. In this sense, he is Elinor's reward.
I agree that Edward's mistakes are very serious: both getting involved with an unworthy girl (especially to the extent of a secret engagement) and to yield to the temptation of furthering an acquaintance with Elinor as if he was free. Both are very immature actions. However, he shows he has a moral "backbone" when he refuses to bow to his mother and sticks to his promise without the benefit of love. I imagine that he has learned from his mistakes.
Elinor and Col. Brandon might be content if they end up married, but love doesn't necessarily develop from this foundation, contrary to romance novels.
