I don't like this game, but I think you hit the nail on the head. This game is pretty much exactly something I could point at and say, "this is so bad it's good".
I found the graphics to be absolutely hideous. The sprites are mostly really weird, ugly pictures cut out and pasted in. I also didn't like the font (though that's more personal preference) and the maps on the sides are just broken.
There's music but no sound. For this, it works.
I think it would be my top pick if the gameplay was just a little better. There's that fine line between "bad but playable" and "unplayably bad", and this sits on the unplayable side. You're supposed to dodge the expanding clouds, but with very slow horizontal movement and no vertical movement it's not actually possible most of the time. You're either almost guaranteed to miss or guaranteed to hit depending on the timing. Simply put the gameplay as designed doesn't really work.
There's also no endgame when you run out of time or hit the ground, which makes it feel incomplete.
It doesn't really come across as "retro" to me. I see what you're going for, but I'm not really feeling it. The intent may be there but nothing really stands out as oldschool when playing it.
I'm not familiar enough with Good Omens to say whether it's a good fangame or not.
It also runs like absolute garbage. I wonder if a desktop build would work better?