Casual Readers discussion

Curious what you think about a length of a series. Some authors can pull it off, keeping it fresh and fun. But other authors seem to drag it out, making it feel like the book is half filler.

What are your thoughts?

Do you prefer series over stand alones?

Do you prefer Trilogy stories over Series?

I personally like series books but when you can see an end to them for example Mortal Instruments a short series. I am less keen on series that just keep running for example the Patricia Cornwell series of books.