"Really, you'd like to use a combination of packages that have been not just tested individually, but tested together, since so much of the complexity in a large software project comes not from its individual pieces but from how they're integrated. Rather than leaving your package system to select the "best" combination of package versions, which could change every day and could be a totally new combination that nobody else has ever tried, you'd like to use a set of packages that has been comprehensively tested by professional release engineers that really know the platform.
That's what the Meteor Distribution provides. Similar to a Redhat or Ubuntu distribution, the Meteor Distribution is a set of package versions that have been tested and recommended for use together."
This drastically reduce the code necessary for example, you don't write form validation code twice, you write it once and show a popup message on the client and throw an exception on the server if something is wrong. Really everything in Meteor works great, there is a really good automatic deploy system (it even deploys to phonegap, also I believe you can deploy your mobile apps to app stores automatically), the API is really small, the meteor packages work great (check out the Velocity testing framework, it is awesome!) and so on
There is one big caveat though, you can't migrate parts of your existing application to Meteor, the only real optional part of Meteor is the View layer, you can discard Blaze and run your own solution. I have had a great time using React with Meteor for example.