Anyone who claims they can definitively predict whether or not Obama will be re-elected at this point is full of shit. No one actually knows.
That said, if I had to put money on it, I'd have to bet that he will be re-elected. As others have stated, the GOP's probable field is weak. The candidates are all either lackluster or seemingly unelectable. People say Obama came out of nowhere so the GOP could have the same thing occur, but that's inaccurate. Obama was a big name on the national scene since the 2004 election. So assuming that there's probably not time for a new Republican star to emerge, we seem to be looking at a field that includes the Romney, Palin, Pawlenty, and a few other joke candidates. Pawlenty could MAYBE be a formidable challenge to Obama, but he's looking like a real longshot to go anywhere in the primaries. That leaves Palin and Romney. We know about Palin. Romney could be a serious challenger to Obama, but he's going to have to warp and distort his positions frantically to the right to survive the primary, and with Palin as his opponent, he'll never be far enough to the right no matter what he does.
But remember, even a lousy candidate can unseat a president with terrible approval numbers. If that continues to decline, it will matter less and less that the GOP has shitty candidates and no vision.