I liked the idea #3. It looks like a Final Fantasy VII settings (which I love) without either copying or recalling FF 7
Also, I've a weakness for sci-fi, so I'd like to see idea #5 in action... but damn! Not with those 4 heroes (who remind me too many FF - 1, 3 and 5 to be precise)
Idea #2 is an emotional pain and this is what I call a traumatic/dramatic plot. You should really work on emotions and interactions between characters. That's really dramatic and with a time limit on... well, it would became a heartache game.
If I were you, if you feel comfortable with character psyche's development, I'll play my cards on ideas #2 or #3 (I was thinking about those soldiers' psyche, people who wake up the morning not knowing if they will reach the end of the day - that is really oppressive, but at the same time interesting).