[mackerel]

I'd like to ask the specific usage of the simple word 'some'. I'm re-studying English grammar at the moment, and I saw the following sentence in a grammar reference book:

'I've seen some good films recently.'

The book just says 'not "I've seen good films recently"'. Then I started to wonder how different they are, or we can't say 'I've seen good films recently' in any situation? etc. Could anyone possibly tell me the difference between them? I looked up some dictionaries but I couldn't find the answer.