The android rating system is pretty simple if you hate the application it gets a one star if you love it the it gets five stars. Also you are allowed to leave a comment as to why you gave it that rating.
The main issue I have against the rating system is once somebody enters a rating even if it was from three versions ago it still shows up. So for example if you started your application three years ago and got a couple of bad ratings they will still be counted against your application today. Even if your application has changed a lot and the issues mentioned in the rating are no longer valid. There needs to be a way to make it fair so it does not turn off new users. For example as a user of an Android device I look at the reviews before downloading an application. I mostly look at recent reviews but if the application has a three star rating I usually stay away. Even if the recent reviews are good. Even though the three stars could have been from months or even years ago.
I think there is a way to fix this that would be fair for developers as well as consumers. If a rating is older than three versions ago it should no longer be counted. Wether it was a five star rating or a one star rating it should no longer be counted. That would allow applications that are progressing and getting better improve there rating over time. Instead of always having really old reviews that are no longer valid sitting around.
The rating system has come a long way. When Android first started you were only able to give it a star rating and leave a comment. Now the developer is able to reply to your comment and you are able to have a dialog. I hope to see it keep improving so it can work for everyone involved.