A good score is one that you are comfortable with. With that being said don't judge your work on what others are getting, you will just drive yourself crazy. If you are happy with what you are presenting, if the image comes across as you intended, then the shot is a success. Eventually, you will see what wins, the type of style and processing.
Obviously you have noticed the compression of the scale because no shot appeals to everyone. It varies by individual, but here's how I take it:
<3 Pretty bad snapshot, extremely out of the box, or an intentional effort at last place (Known as a "Brown Ribbon", or "Brownie")
4-4.5 Pretty poor, or extremely misunderstood and under appreciated.
4.5-5.0 A good effort that shows some knowledge, but still lacking in some major way.
5.0-5.5 A decent effort that just did not blow people over. No shame in a 5
5.5-6.0 A good shot that appealed to the majority of people, or had very strong appeal for a smaller group. Despite people moaning about scores in this range, it is doing well and is usually a mid-pack or higher placement in most challenges.
6.0-6.5 A really good shot with broad appeal. Most members are thrilled to hit a 6 in any challenge.
6.5+ Killer shot, this getting into ribbon territory.
That is an excellent break down. Thank you for taking the time to do that. I am definetely not in it just to get high scores and I will have many more bombed shots in the future but I like to see what people are generally feeling about the photo. Thanks again.
Personally, I'll look at my percentile in a challenge more than the actual score. Some challenges just have really low scores, and some challenges have SOOOO many entries. For instance, I'm still really happy with my Ansel Adams entry, even though I've had others that have placed higher, but it was really up there percentile wise.
But really, I always try to view my images in terms of how successful they were at portraying the subject and the moment, and if I learned a new technique or approach. I've also had entries score terribly, but was happy with the outcome because I believe they achieved what my end was or I learned something from them. To me, the ability to control an outcome is far more important than the score. Try to view your scores in relation to what you're more comfortable with too. I'm more of a landscape shooter, so I naturally have higher expectations for those shots than other genres.