5 stars simply because it is a lot better than so many games with 4 star ratings.
The game has bugs, but the developer is active in trying to track them down and solve them.
There is often someone in the game to help if you ask, and a generally great community.
There are plans to expand many aspects of the game after critical bug fixes are done.
Biggest problem now is a lack of 6 stars for when the game gets even better.