Weird. I was just looking at Jehan yesterday!
I think I like it, although I wouldn't consider using it, both for pronunciation reasons and my aversion to John names. It does seem light, sunny, and sweet in a way Jean does not. It's certainly different, and I love its medieval feel.
Your Isidore images make me smile because mine are so far in the other direction. I find it so dark and almost-sinister.