What is the difference between evaluative and descriptive adjectives?
Evaluative adjectives tell about something that can be measured and compared.
For example If one person is 1.6 m tall, and another is 2 m tall, we can say that the second person is taller than the first (or even the tallest in a group of people)
Descriptive adjectives tell about properties that cannot be measured. They can be bound to colour, material, etc.
For example if we take adjective wooden. We cannot say that one thing is "more" wooden than the other. These features cannot be compared so the adjectives do not have comparative or superlative forms.