Jonathan Strange and Mr. Norrell is one of the great books of the last half-century. It's a stunning achievement, the kind that seems like it would take an author's entire lifetime. It begs rereading to connect all of the dots, and craving more.
Piranesi isn't that book. It's an entirely different book, so much so that it's hard to evaluate on its own. On its own, it's a very good longish novella, meditative in a way that was perfect for the early pandemic times when it came out. Reading it during lockdown was a lot to handle.
So while I know it was very good, I mostly remember disappointment that it wasn't better. Unlike the OP, I felt that it was structured as a mystery, one whose result wasn't entirely satisfying. Strange was set in awesomely consistent magical world (including consistent inconsistencies). Piranesi rather hand-waves at a magic that doesn't bear any scrutiny but bears too much weight of the plot to wave away.
It begins so, so well, and the first half sets up an excellent enigma and rich world. Maybe others will feel that the second half carries it off better than I did; maybe early pandemic wasn't the time to read it.
I really like your analogy. I wouldn't have put it that way, but it beautifully evokes what the novel felt like to you. It's a helpful case where I can say, "Ya know, if it's not grabbing you 20 pages in, maybe don't bother." (I resent all those times people tell me, "Oh, you just have to slog through the first novel/first season and then it gets good.)
I happen to be re-reading Jonathan Strange and am enjoying it even more than the first time.
Honestly, all those meditations on the infinite start blurring together after a while.
Has Piranesi comparable vibes?