Winx is a great show for teens and pre teens
It's target audience is for children, but some older teens even enjoyed it's funny, adventurous tone. The characters are funny, lovely, and you can picture yourself as either of them. The storyline and setting are well built and the plot from season 1 - 4 is well built. However after that, it gets a little complicated and becomes strange and the plot takes a changes as more seasons come by.
The transformations are beautiful and most of them relate to each of their characters. Overall in my opinion, I have watched it over probably ten times and enjoyed rewatching every time.