Simon was my favorite character in the original Firefly series, and one of the reasons was the snark. The sarcasm. The brilliance at cutting someone down with a few carefully chosen words.
This skill wasn't really in evidence in Serenity, and I miss that, even though I understand why. A movie is not a t.v. series, after all, and there are big limits to what you can do with only a couple of hours. Some things that were part of the t.v. series are not going to be part of the movie, simply because the form can be constraining.
And part of the lack of Simon Snark is probably because he and his favorite target, Jayne, just didn't interact a whole lot. I hope that if there are sequels, we'll see a little bit more interaction. Otherwise, I'll simply be forced to re-watch "Ariel" and "Trash" over and over again ^_~