I love Portishead, and so when I purchased 'Third' I sat down excitedly to listen... and, like many others, was disappointed. I put the disc aside and never gave it a second thought for several months. After that time, I thought I'd give it a second chance. That time, 'The Rip' sort of grew on me. Subsequent listens revealed the awesomeness in 'Machine Gun' and 'Magic Doors'. Finally, the entire album as a whole revealed its beauty to me.
I'm not sure if you just have to be in the right state of mind for this one, but there is an awesome album in here. If you didn't like it the first time around, give it a second listen - it just might change your mind!