I like the idea of a theme, I'm just not convinced whether there should be two themes.
Going green may be fun, if it was also somewhat hardcore (give them no luxuries, make them pedal for water for a shower, ban smoking, have a duck pond instead of a jacuzzi, that sort of thing).
Secrets and lies may be fun, but it's got a short shelf life. After a few weeks it could become boring.
Perfect world... if there are secrets, then let the viewer in on them, otherwise it's the fail we've seen last couple of series, where it looks made up on the spot to protect/ hinder a HM.