Pathfinder 2 isn't going to do well regardless of how good a game it is, but it's shaping up to be a pretty awful. There is no one especially horrible design choice, but rather a whole pile of small, bad choices that indicate poor management and a lack of direction.
How can I tell? The key is that creators, which includes everyone from artists to engineers, require the firm hand of management to stay on task and put together a coherent product. If you do not do this, your creatives will destroy you. They will continue adding ornaments, frills, doo-dads, and gee-gaws to your product until it is a total mess.
PF2 contrasts with 5e, which has been a tremendous design success because Mearls' team worked from a "less is more" philosophy. When they ran into a problem, they solved it by removing or simplifying features, or rebuilt underlying structures. This is much more difficult than adding complexity and features. The final game was much simpler than the initial test packets (with their "martial dice" and other dropped features), and has benefited for it.
The Paizo team never really talks about any coherent vision or goal. Instead, the language that comes up the most seems to be opening or increasing "the design space" and giving the creatives more ways to play around. This should set off a ton of alarm bells...designers do not need fewer constraints compared to 3.5, they need more!
An example of where PF2 design is falling apart is
spell heightening (just look at what a mess the new Heal spell is). In 5e, many spells may be "upcast" by using a higher slot. Each additional level typically adds another damage die or two, adds another target, increases the duration, or the like. In PF2, there are different kinds of heightening. Perhaps you gain something per slot, or per two slots, or the gain depends on both how many slots you increase and how many actions you spend, or perhaps there's a single large gain only at a specific higher level.
Another example is the "3 action economy." This initially sounded promising---getting rid of Swift, Standard, Move, and Full actions in exchange for just "actions" made it sound like they were adopting the KISS principle. But as we learned more, it turned out that they were actually adopting an action point system. AP systems are fine, but they're significantly more complex that simple action systems. So while Mike Mearls over at WotC regards bonus actions as a design failure, since they added what he considers unnecessary complexity, the Paizo team is gleefully cranking out all kinds of ways to modify things by spending 1, 2, or 3 action points. Not only that, but they're writing feats and features to introduce exceptions to the AP system! So a wizard will get four action points, one of which can only be spent to concentrate on a spell. A fighter can take a feat so that moving twice and attacking costs only two actions.
What they're producing is chaos. The less consistent the patterns are, the more time players will have to spend parsing rules text to make sure they get it right. The more complexity and exceptions there are in the rules, the more places overlooked interactions will cause the system to break down (this is why 3.x was an unfixable mess). "Opening up the design space" to give your creatives more space to play around and fewer constraints or patterns to cleave to produces design messes.
At this point, I'm expecting PF2 to be a disaster for Paizo. It won't even make Pathfinder fans happy, let alone attract anyone from 5e or draw in new players to the hobby.