Depending on your morality both endings can be good for New Vegas. My first playthrough I went with a 'good' character who helped Mr. House achieve his ends. I decided "stuff it, I'm an enforcer for perhaps the most brilliant mind on the planet".
It actually paid off. He's not insane, he's the exact opposite, the most sane individual you'll encounter. He measures every situation and thinks of the best long-term result - having "lived" for as long as he has probably grants him a better understanding of long-term planning.
In the end?
I hope there's an expansion pack that allows you to play after the completion of the game and see the effects of your actions in the game world beyond slide shows.
There won't be. They've said that all DLC will take place BEFORE game completion, there won't be any DLC opening up content after main quest completes.
That doesn't mean that they wont make a patch OR incorporate a fix into the Downloadable content to open up game-play after the main quest!
(If enough people post on there website to make game-play after the main quest they will add it, they do have a commitment to delivering superior titles to gamers worldwide as does every other company!)