Context: I have GM'd for an investigator from levels 1 through 9, and three campaigns overall.
The DM apologized for not realizing I was an Investigator and needed some additional prep opportunity baked into the game, but he shouldn't have had to.
The investigator benefits from having setup time, but it isn't necessary to the class working.
If there's a mystery of some sort involved, and if you have the opportunity to prep with some investigation, then you can use your Int for attack rolls
You don't need any of the above, you can ALWAYS use Devise a stratagem (and should be most rounds!). Importantly, you also don't need there to be "a mystery" in the literal sense, you just need to declare a concept or individual you want to investigate during exploration mode. Investigators can be played in any style of campaign.
2 hours isn't enough time to showcase a system properly. I imagine you were playing a Pathfinder Society Bounty. These play VERY differently from a home game due to the public nature and time constraints. Even full PFS games tend to gloss over mechanics and present a narrow railroad adventure for the sake of efficiency.
But I also needed an action to power myself up for a damage bonus, and in a battle that only lasts 2-3 rounds, it's not worth trading an attack now for a small damage boost later. So basically the whole setup was a more complicated way to get two attacks, sometimes, maybe.
It is absolutely worth trading an action for the damage bonus. Most combats should last 3-5 rounds, 2 rounds is extremely short for a PF2 combat. Keep in mind that because of MAP, your attacks after the first are significantly less valuable. Move, Overdrive, attack is far more useful than move, attack, attack in most cases.
Finally, complexity. A demo D&D character sheet is one piece of paper, single-sided; maybe two if you're a spellcaster. Every PF character sheet was two pieces of paper, at least the first of which was double-sided. And the class features are dense. I had to read both of them very carefully (while the game was going on) to figure out how all the pieces interlocked.
This is absolutely a reasonable criticism. PF is not newbie friendly if you're coming in blind. It is not as fun for one-shots compared to campaigns where you can really learn your character, in my opinion.