Dressage is judged as a series of separate movements according to a scale:
0 - not performed
1 - very poor
2 - poor
3 - fairly poor
4 - insufficient
5 - sufficient
6 - satisfactory
7 - fairly good
8 - good
9 - very good
10 - excellent
There are directives listed at the top of the test, and with each movement which become increasingly more difficult as the levels progress. For example in training level the horse is expected to be "accepting the bit", and in first level they must be "on the bit".
An example of how a movement may receive different scores in training level on a 20m trot circle.
If the horse is misbehaving/cantering/bucking depending on the severity they can receive between a 1 and 3. If the horse canters the whole circle, technically the score should be 0 (as a trot circle was asked for), but most judges will give a 1 or 2.
If the horse is against/above the bit very vigorously, a 4 is given.
If the horse is above the bit, or if the circle is very wonky, and rhythm mistakes, a 5.
If the horse is accepting the bit to a satisfying standard and the circle shape is good, or if the horse is accepting the bit well and the circle is wonky, with decent rhythm, a 6.
If the horse is accepting the bridle and the shape is good with a fairly good rhythm, a 7.
If the horse is showing a good acceptance of the bridle, good rhythm, good shape, and 8.
If the horse is truly round and through with a very good contact, rhythm and showing great swing and lovely forward motion - this is when the 9 and 10 get pulled out!
Of course now there are half points which are more helpful to those on the lower end of the scale. If it is between scores, a half point is awarded. I see mostly 5.5 and 6.5.
So - "satisfactory" will never get you a 10. It must be exceptional. The difference for me in the scores is below 3 is verging on scary/naughty/being rung out, a 4 is sketchy as, a 5 is almost there, a 6 checks all the boxes, a 7 is nice to watch, an 8 is a pleasure to watch, a 9 is just absolutely lovely and a 10 takes your breath away.
Hope that helps explain!
They say money doesn't buy happiness -- well happiness doesn't buy horses!