Qual è la differenza tra I was surprised by how much I enjoyed it. e I was surprised how much I enjoyed it. ?Sentiti libero di rispondere con un esempio.

"I was surprised by how much I enjoyed it." is a statement. There is no doubt of your surprise.

Example:
A: How did you like the movie?
B: I was surprised by how much I enjoyed it.

"I was surprised by how much I enjoyed it?" is a little more vague. In this version you may be really, really surprised you enjoyed it. It could be implied that there were many indicators that you weren't going to enjoy whatever 'it' is.

A: How did you like the movie?
B: I was surprised by how much I enjoyed it? I didn't think it was going to be good at all. The trailer wasn't that great. But the movie turned out to be really entertaining.

Feel free to ask for more clarification!