I'd echo everyone else on how awe-inspiring this building is. One thing that's particularly interesting is that, while the outside is extremely cluttered and ornate, the inside is almost spare by comparison, and achieves a level of immersive awe that I've never experienced before.

In that sense, the building is almost too successful - a church is meant to glorify God, but there's no disentangling the Sagrada from Gaudi. You cannot stand in the building and not feel a sense of awe for the mind that created this, and the building is far, far too famous to ever be a servicing church. It was such an interesting contradiction of an achievement - it's such an incredible artistic accomplishment and so successful in its intent to inspire and as an act of devotion that you just cannot look past the finger to see the moon. The artist eclipses the subject.

(As an aside, Orwell makes mention of the Sagrada Familia in Homage to Catalonia, and it's an incredible paragraph: "For the first time since I had been in Barcelona I went to have a look at the cathedral – a modern cathedral, and one of the most hideous buildings in the world... Unlike most of the churches in Barcelona it was not damaged during the revolution – it was spared because of its ‘artistic value’, people said. I think the Anarchists showed bad taste in not blowing it up when they had the chance.")