I get the idea of this puzzle. The theme is PGTHIRTEEN, and the letter pair of "pg" appears thirteen times in the grid, including in the rating. Which, by the way, is really PG-13, isn't it? As we learned in Patrick Berry's Sunday puzzle? But glossing over that little detail, the placement of so many PG's leads to some truly ugly fill.
Just look at the first corner. There are two abbreviations, one of which is really questionable (ANS), and three foreign names, not to mention a brand name (RAGU) just below. 1A: Leader with an -ism (MAO) is saved by the cute clue, but not above a C-. And it just goes on and on.
The next section has your random Roman numeral (CMII), along with two abbreviations (one of which, ASSN, is clued by a cross-reference to another abbreviation!), and yet another foreign name. I could blather about this for a long time. AAR? UTENN? REOIL?! LIC!!!??? And there's a bunch of old-time crosswordese as well. I had a feeling I'd find IRES in here.
I liked INTOODEEP right next to KEEPGOING. After all, once you've got that far, what else are you going to do?
And that's how I felt about this puzzle.