Hmm, I wouldn't call the rest of their discography "dull" by any means, but I can see how it would be someones favorite. I happen to like the Soft Bulletin quite a bit and think it may be my favorite Lips album: There are a lot of Lips fans that will go with Clouds Taste Metallic: If I had to choose just one though, I'd go Soft Bulletin. Hard choice though, hard enough that I think calling their discography "dull" isn't apt. But that's just me.
I guess dull isn't the appropriate word. They just haven't made anything that i like as much as Yoshimi. I don't think it's something i could ever describe, Yoshimi touches me in a way their other music doesn't. Not to say that everything else they make is bad. There's the stuff i like, the stuff i don't really get, and Yoshimi. That's why i used the word dull... It's hard for me to listen to their other albums objectively, knowing that Yoshimi exists.