I'll briefly give you my main thoughts on what I thought when I first read The Apocalypse of John when I had only read the New Testament, and then again when I read it a year later after having read The Old Testament and some Apocrypha.
On my first reading of it, I was very stunned by the ingenuity and bizarreness of not just the symbolism, but the manner is which the symbolism was presented. Symbolism was nothing new to me, of course, but the imagery and method of conveying the imagery was very disorienting.
For example, I found Revelation 13:3 to be a particularly striking moment. Revelation 13:1-2: "The dragon stood on the shore of the sea. And I saw a beast coming out of the sea. It had ten horns and seven heads, with ten crowns on its horns, and on each head a blasphemous name. 2 The beast I saw resembled a leopard, but had feet like those of a bear and a mouth like that of a lion. The dragon gave the beast his power and his throne and great authority." This is already a Surreal enough scene, so heavily steeped in obscure metaphor that to imagine it literally is like a fevered dream, but then 13:3 reads: " One of the heads of the beast seemed to have had a fatal wound, but the fatal wound had been healed. The whole world was filled with wonder and followed the beast."
What does this mean? It's so utterly bizarre and specific. It's no doubt a very pointed metaphor by the author, but it in and of itself is so strange. A monster raises itself from the sea? Okay. Nothing too weird, even if it's a weird monster, but then there's such an unexplained little detail like that? That really takes it to another level for me.