The (IMHO) important bits:

TLDR:

Our continuous internal reviews and beta test groups have highlighted areas that we need to focus on more, mainly performance and content

From the FAQ:

Is the game canceled?
No, the game is not canceled.

What happens to pre-orders?
All pre-orders will be refunded in the upcoming weeks. The option to pre-order the game will be removed and the bonus will instead be added to the base game for all

Is there going to be Early Access or Beta Access to the game?
There will not be an early access or extra beta access right now

In the blog there are the steps to how to get the refunds, I'm not copying them in case they change.

As they say, A Delayed Game Is Eventually Good, But a Bad Game Is Bad Forever ^/s?^

I loved 1 - but 2 didn’t make any sense to me. Slapping 3D on it didn’t seem like something it needed, and it makes it a very different game. Plus, it’s not made by introversion - that’s where 95% of the humor and novel game mechanics came from.

Prison Architect 1 was amazing, up until Paradox bought it. I didn't have high hopes for PA2 (not like I was going to play it anyway) but I definitely wasn't expecting this

I really loved the first game, but have zero faith in the sequel. I think the whole 3d rework makes no sense, and on top of that, it’s led by a company, that’s historically made the worst choices in every aspect of development