Meeting members of the decemvirate when you're a low-level mook is weird and awkward, especially considering you already know everything you need to.
There were many skill checks. This was fine for me, because I was playing a rogue. Not so good for others.
There was a research scene. This is an optional subsystem that involves making a million skill checks over in-game hours. Woo, the excitement.
The biggest monster showed up during this research scene, and we got no warning so we didn't have weapons drawn or shields equipped. The monster did not have to spend actions equipping its weapon and had high initiative. We had predictable (unshielded) level 1 ACs of 18, and it had +12 to hit (for d12+5 base damage), so it dropped the best fighter before they got to act. After that it was an extremely predictable TPK.
What's bad about this is not the TPK. It's the utter predictability of it. It showed up with no warning, had high initiative, and had a lot of HP. Plus it had a 1/4 chance of critting and a pretty good chance of insta-killing anyone it did crit. And what's really bad about all this is that level scaling is built into the game mechanics. It's not like a PF1 random death from a mook with a greataxe critting - the monster just isn't down-scaled if you're level 1. The system arithmetic is very predictable, as are the consequences.
Conclusion: the boss needs some level adjustment, a round's notice that the encounter is coming so the martial characters don't waste the first round drawing weapons, and maybe a smaller weapon. After that the scenario could use some tweaking on the skill check DCs.
This one is kind of cool. The monsters are fun, the world flavour is good, the visuals it conjures up are neat. So why the low rating? Because the very first thing that happens is that the entire party gets to make a save-or-suck, and if the wrong person or people fail, succeeding could be impossible. There's a potential TPK just from that. And that is on its own such a terrible piece of punishing design that you should just avoid this one completely.
I'm with wakedown on this. It's not awful, but it could be a lot better, and the way everything is laid out definitely works better for some characters than others. We played it a few days ago, and the Dwarf character barely got to do anything (I think he made two attack rolls all game) because he wasn't at the front and he couldn't get there quickly enough to participate. If some of the encounters had had multiple waves of monsters, so the quicker people killed the first wave and then the slower characters got in on the second wave, that would really improve things.
Also, the difficulty could be raised and that would probably help. Admittedly not having seen the monster tables I don't know if we just rolled the easiest encounters, but it's hard to see any interesting tactical depth in a game if you just roll over the opposition without doing anything more clever than attack. We weren't playing an especially optimised party, but we never fought more than two mooks at once and they went down in less than two rounds every time. I soloed an encounter in a tunnel just because I had a faster move rate than everyone else so I was ahead. It could have been an exciting and terrifying moment where rushing off ahead got me in trouble. Instead it was just a matter of swinging twice and thinking "is that it?".
"Is that it?" sums up the adventure, really, though it's harsher than I would be. Sinister gillmen visitors... are actually not hostile. Mook enemies are actually... not dangerous enough to be scary. Even the minotaur fight wasn't exciting, because all the difficult terrain made it just a matter of seeing how far you could get and keeping on shooting.
It does the intro stuff adequately. It brings across the world flavour well. And Janira is definitely a fun NPC (we were sad when she bled out one round before getting a potion). But it doesn't really sell the game system, because you don't particularly get to engage with it.