Even positive feedback can be constuctive, as well. For instance, instead of saying:
"I just jizzed in my pants!"
you could try saying instead:
"I just jizzed in my pants because the colour scheme reminds me of FS1, which creates a nice connection between FS1 and FS2."
or something to that effect. It's good to know why you like something, both for the artist and the critic.