Again: I haven't listened to this album. But as far as I know, it contains more sounds and musical pieces on it, rather than "real" songs. So what's wrong with calling this "experimental" ?
Well, it puts us into a debate of what's experimental and what's not. But experimental has the tag of 'don't expect too much from it', or 'let's not take this all too serious'. And I refuse to accept that particular tag. It was a commercial release. Quote from Bruce Spizer: "The February 1, 1969, Rolling Stone
reported that Tetragammaton ordered 200,000 copies of the album. Company president Arthur Mogull stated that he would be 'stunned if it didn't sell a couple of million'.
What I'm trying to point out that I find it remarkable that John fans let his solo carreer start in 1970 with the release of Plastic Ono Band, completely neglecting the three albums he released before. I'm not sure whether John regarded these albums as experimental.
On a sidenote, also from Bruce Spizer's book: "When EMI head Sir Joseph Lockwood warned John that the cover would ruin the Beatles image, Yoko told him it was "art". Sir Joe replied, "Well, I should find some better bodies to put on the cover than you two. They're not very attractive."