I can see why it got so much flak, even having just played the opening vignette.
It was sold on the premise of being a D&D inspired game, but delivered some weird-ass crazy mechanics thing that kind of looks like an infinity engine game but also entirely doesn't.
And if you're going to flop out a whole raft of completely new systems then it might help the player if more time was spent in tutorials of what is going on.
I still have zero idea what endurance either is or does and I've been playing for hours, and while it's clear it's the primary mechanic, I have zero knowledge of what is happening to my endurance during combat and what, if anything, is going on when I take a hit or dish one out.
At this point in the game I just do what one normally does and the enemy seems to fall over and the battle is won. But what I did on a mechanical level I have no idea at all.
And I chose a character who uses Focus, another seemingly new and inexplicable mechanic that is crucial to the game. I had to google what Focus even is and why it is I only have 7 of it and why I can't even use my starting skills.
The game has tool-tips for lots of things, but not Focus, this seemingly crucial stat. It doesn't even mention it on your character sheet. The only indication that I have any focus at all is this little round number on my portrait during exploration and combat. Clicking it doesn't take you anywhere and there's no indication of how to increase this number.
Even googling didn't help because everyone who asked got told the mechanical answer, no-one answering understood that the problem was the lack of in-game communication about this mechanic and so the detailed and factual answers meant nothing to the asker, as they didn't have the base knowledge of what it was in order to understand a detailed answer of how it works or what it is.
And the whole thing about everything lasting for "seconds" is really off-putting. It makes it so much harder to understand quickly and easily the difference in power-level of a spell or effect. The descriptions of everything read like gibberish.
None of this is a problem once one is fully experienced with the system, of course, I mean, D&D is extremely confusing the first time you play it.
The difference is, most of the people who rushed to buy those first Infinity Engine games already knew the rules and the complaint was more that the computer versions left out lots of minutia. With PoE, literally no-one has ever played these rules before, so the only way to learn them is to play the game fully... at which point you've then already played the game.
And so, naturally, people were just frustrated that they didn't just use OGL or something, the people being mostly D&D fans who thought they were funding another D&D-like game.
It just gives off a very off-putting first impression. It makes it so much harder to placate your core audience that had... payed for something in advance. I didn't, so I'm not that bothered. To me it's just another random RPG