I never liked this song much either.
Most Beatles songs are little pop music masterpieces. Great verse, great chorus, great bridge, perfection from start to finish. AYNIL on the other hand is IMO little more than a clever hook (which it definately is) that was expanded into a full song. It's a bit of a gimmick tune. This approach might have been perfectly fine for 90% of all other pop groups, but for the Beatles it was a bit below their class.