I started loving this series because of it's pop american style with fast cuts, jump sequences of editing, humorous quips and sassy dialogues, and the great filming of the locale. It became monotonous after 2-3 seasons. Season 4-5 were particularly drab and the characters became routines, conservative, rehashes. Seemed forced. Again from 6th season onwards things started moving up. Season 7 was a fantastic one, but it totally deviated from it's main theme. Probably that's for the better. It became serious. Lots of grandstandings, moral ethical dilemmas for the main leads.
Fiona's character changed drastically to being choirgirl almost, from a funloving trigger happy girl. That and Sam also turning into a homebody, changed the scenario of the series. It hurt it.
Anyhow the final season , though different in essence , recouped a lot. Lot of us shed tears for the sacrifices.
Michael became sterner and his mind was tortured so much that he couldn't find the right way. This inevitably went towards finishing off the series. There was no way forward after this.
They always had a small side story taking the show forward in between the starting bigger story and ending with it. The smaller story took the characters forward which somehow could adjust and settle the characters in our mind. This stories became repetitive, which was bound to happen. So probably it was required to put in a big black mission in the middle of the whole season and finish it off.
Finally difficult to believe that these group being divided now will remain so forever. I want them seriously to have a get together again and lots of new adventures.