I think a very careful balance needs to be struck, because so many projects can overstay their welcome. For example, I loved "Smallville" as a whole, but that ten years of stories could've been done in six if they'd cut all the constant delays and sudden twists that went nowhere.
Another show I really enjoyed was "Roswell", but it started suffering low ratings almost immediately. The fans managed to keep it alive for 3 years, but nothing lived up to what it could've been. There was constant bickering behind the scenes, about what direction to take things in, and it screwed up the entire ball of wax.
I agree with "Sarah Connor Chronicles" being a severely missed opportunity too; so many stories either got slashed or played out for way too long.
Sadly, it seems like money's the primary concern for most people in Hollywood, and they could care less about what truly reaches people in a story. I actually feel sorry for actors like Summer Glau, who keep getting involved with projects that are shelved without explanation. "The Cape" had an interesting premise, but again, greed got in the way.
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God, guns, and guts made America; let's keep all three.