Wonderwall, which the title of the song alludes to, is a 1968 psychedelic film in which an older scientist discovers that he can see through one of his walls into the neighboring apartment. He, of course, falls in love with the young woman who occupies that apartment. I've seen the opening bits of the movie and the soundtrack is a series of weird Eastern sounding pieces by George Harrison. I doubt that the film is anything more than somewhat tedious (I gave up on it myself).
I've always liked the song, though. ((What's the Story) Morning Glory? is a pretty solid album on the whole. "Don't Look Back in Anger," which follows this song is especially good I think.). However, I have always been more of a Blur fan than an Oasis fan for the most part. Blur's Leisure is my favorite British pop album of this period, strange and moody as it is.