Two things will determine who wins:
IND - If CBS and other polls that have Romney up double-digits with IND proves to be accurate Obama is history. Personally, I think it will tighten, but at a double-digit IND lead would be a tidal wave that a state-by-state strategy couldn't fend off.
PARTY TURNOUT - Tied to the above. If the GOP enthusiasm is as high as polls show, Obama again is in deep trouble. If he loses INDs (even by single digits) he needs to pull several percent more DEMs.
Other than that it is all guessing. But if Obama can get a 4%+ advantage in party turnout and keep Romney around under +6 with INDs he will win. If not, he will lose. If he does he'll take all the battlegrounds IMO. If not, Romney will take them.