Definitely worth a visit!
By A Yahoo! Contributor, 7/13/08
You can't claim to have seen Barcelona without taking an up-close look at Gaudi's work. From the outside, I wasn't very impressed by Casa Mila/ La Pedrera -- it seemed almost grotesque to me. It's only when you enter the show apartment (furnished as it would have been in the early 1900s) that you appreciate Gaudi's genius. The rooms really flow into each other, and have wonderful natural light. I have no particular interest in architecture, but it was fascinating to see how well the space is used.
The exhibitions in the attics (composed of wonderful catenary arches) are very effective in showing how Gaudi's careful observation of the natural world influenced his designs. And from the attics, you can get out onto the roof terraces, with their weird and wonderful chimneys, giving a great view out over the city.
I don't remember the entrance fee, but audio guides in a variety of languages were included with it, and these added a lot to the experience, giving lots of extra information. I'd definitely recommend a visit, but go early to see the show apartment, to avoid crowds.