Sounds like a cool idea, a few points to think about though
*How will you keep play intresting, being on your lonesome trying to kill an island full of baddies will be hard and frustrating work if theres alot of die and retry.
*To get the cleverness in the AI to say "he's a spy" etc will need a fair bit of scripting, I should expect.
*You would have to have a good background story, how about instead of investigating something sinister (sounds very resident evil ;D) looking for escaped war criminals who could be hiding on the island, then you could call in support/ bomb strikes etc or choose kill them yourself and escape from the hostile island.
Keep up the work hope something i've said has helped in someway.
GI-YO