My roommate and I watched Serenity when it came out in theaters. At this point I had never seen an episode of Firefly, or ANYTHING by Joss Whedon. Later, he bought the DVD series and the movie, and one weekend we watched ALL of it STRAIGHT with a break for lunch and dinner. Great 15 hours, right there.
You can bet that had the series continued, there would have been more deaths of the crew, and they would have been replaced by other quirky personalities. In Buffy, characters die or leave in horrible and amazingly sudden ways, but always in a way you can see happening in hind sight. Angel goes the same way, people get hurt, physically and emotionally, and sometimes people die.
Usually when you start to like a character too.
Joss Whedon takes his time developing characters, and his dialogue is great. There are few episodes where there’s not something I’ll laugh at.
So yeah, consider me in the camp of people that are angry the actual series won’t be completed. The movie changed enough from the actual series to let people in, but also made it so that there couldn’t be a particularly smooth segue into it from the series. Still liked it though.