Why It's Terrible - "Second verse, same as the first." This iconic line sums up the song's writing for the second verse is literally the same as the first; and those are the entire lyrics of the song. It's a gimmicky novelty of a song, based around one joke about Henry VIII being the eighth man named Henry married to this woman in the song. The joke is so central to the track's existence that the only way for the song to actually last long enough to be a commercially viable piece was to repeat it three times in total to fill up the run time.
Why I Still Like It - Despite the song being a joke, I actually find it funny, charming, and catchy. The verse is memorable, fun to sing, and is propelled by a rather brisk rhythm section and a simple but fun guitar riff and solo. It's also just under two minutes long so it by no means overstays its welcome.
Final Notes: "I'm Henry VIII I am" is a ridiculously inane song that's stupid fun with an emphasis on both of those things. Having one verse repeated three times is indeed stupid, but it's a fun verse to hear and sing. It could easily be a much worse piece than it is but the arrangement actually has some merit to it and stays fun for repeated listens. It also will get stuck in your head for hours if not days at a time.