I've always liked the a-side. If you don't like John singing about himself, you probably don't like most of his post-Beatles music either. Some may call it "self-indulgent", but a whole lot of people really eat up all that introspective, personal stuff. When a person makes art about something that they themselves are feeling, it tends to feel more powerful and intense to the end viewer/listener, especially if it's done right. Take Paul for an example of the opposite end of the spectrum. He almost never puts himself into his music. He sings to universally appealing things, or he tells stories about other people. This takes a different kind of talent, and has a very different, but still enjoyable, effect on the end viewer/listener. The only pieces of himself he usually put in his music is that he loved Linda, and that was painfully obvious to anyone who saw them together when she was around. You don't know about their fights, which they undoubtedly had, because they chose to keep them private (which is valid, of course; as I said, it's just two different styles of music and also of life). The one time he actually writes a song about something personal, when he says he loves John, everyone's jaw drops.
The point is, some people like one style more than the other. I happen to like both, and I like this song and the way it allows John to laugh off his frustrations with people driving him nuts all the time. I also think the Christ/crucify joke was more a joking jab at himself than a cocky likening of himself to Jesus. He was referring to his earlier media gaffe. At the same time, the likening was probably ironic; by comparing himself to Jesus and the horrible troubles he went through, John was telling himself that his comparatively minor annoyances weren't that bad. If he were serious about thinking his life was as rough as Jesus's, the song probably wouldn't be so upbeat and fun-sounding.
As for the b-side, I don't know who played the bassline, but I believe George played just about all of it except the drums on the demo, which appears on Anthology, so if Paul played it he was taking instructions from George.
I really love this song. It sounds like the sonic equivalent of riding in a horse-drawn carriage where the horses have been spooked and are running frantically, and the lyric is just as scary. I think it's a really fun song, and I don't think it needs a chorus. I think a chorus probably would have hurt the song, in fact.