I've got nothing against a good gimmick. And there is something impressive about a puzzle that uses only one vowel per row, in order of AEIOU, then does it again, and then again. So I acknowledge the artistry of the gimmick. But that's what it feels like in the end, a gimmick, in large part because of the compromises that have to be made to make it work.
Why might I have made that error? Well, let's see. 35D: Make a sibilant sound (SISS). This is not a word. This is not a sound. This is not anything. It has no place in the crossword puzzle. I had SsSS. That at least, somewhat makes sense. I'll admit that what I had at 34D: Call in place of a nudge (PSST) was PiST, and I knew that couldn't be right, but I went with it for some reason.
There are some fun answers, especially in the long acrosses. PHILIPIII is crazy looking. THECREEPS is good. I love POLTROON. It's right up there with "Nimrod" from yesterday. AAAMAP is barely acceptable, but I like the way it looks. 5D: Person with lines (ACTOR) is a cute little misdirect.
So, on the whole, okay, but that section mentioned above ruined it.