First, yes, I think you should email them. If you enjoyed their class so much, then it is likely that quite an ammount of work, and effort went in preparing them. Learning that it was enjoyed, and that this work and effort did not go to waste is probably going to make them happy.
If you want to avoid any misjudging on your intentions, you should specify a few thing you really enjoyed in his class.
Hello professor X
I'm Emailing you to let you know that I found your classes particularly enjoyable. I especially enjoyed your lessons on X and Y, and I learned quite a bit during the lesson on Z.
Telling them about specifics parts of what you enjoyed will show that you are honest, and, more importantly, that their classes stuck with you.
All in all, definitely email them, everyone likes having their work aknowledged from time to time.
