It depends on your point of view.
The fact, as I see it, is that no one and nothing will ever solve all of our
 problems at once, now and forever.  People will always be people.  You can't
 wave a magic wand and fix it all.
Yes, there was another war...but had the Shadows not been stopped by our
 characters, there likely wouldn't have been a human race at ALL anymore.  
Yes, there was a war, and many died in it...as tends to happen in war...but the
 nominal right side in it came out on top, which would not have been the case
 but for Garibaldi's simulacra giving them a leg up on things.  
We have had, continue to have, and will always have wars, and grief, and
 struggle...we will climb up and fall down...but each time we climb a little
 higher, and in the end, we *do* build the world that our ancestors would have
 wanted for us...we *do* leave the cradle at last, and we take our place among
 the stars teaching those who follow us.
For my money, that's as happy an ending as we or anyone can ever hope for.
 jms
