There are a lot of bad reviews for this game. Mostly, those are written by angry people who evidently lack the capability to understand what "in development" actually means:
This is Early Access, so don't expect a complete game! Also, don't expect a beta version (= basically finished game that is in the last stage of testing).
What you will get (as of right now), is an alpha version that is still undergoing a lot of change.
During the last years, the devs of this game have mostly worked on its engine, so there wasn't much progress that you could actually see (except from the regular dev blogs and patch notes). Right now, they are however much closer to the point where they can start to add actual content, so you will probably be witnessing the most interesting part of this game's development.
In terms of what Early Access is supposed to be, Castle Story is a great offer. The actual game is really fun (even though it is still very basic) and Sauropod cares about communicating what they are doing.
Just remember: If you buy the game right now, you don't pay for a playable game but for the possibility to be part of its development( and the promise that eventually you will get a complete game).
Personally, i have so far enjoyed this experience and it has absolutely been worth the money that i have paid.
If in the end (and i am really optimistic that this will be what actually happens), i also get a nice game that alone would have been worth the price, it's an awesome bonus.
If you can identify with this way of thinking and the concept of Castle Story looks fun to you, this is basically a no-brainer...
If however you build up you expectations based on wishful thinking instead of what is actually promised in the game description, save yourself the disappointment and everyone else yet another rant about how this game is a total scam because it isn't finished yet!