After seeing the gameplay for Kingdom Hearts 3 and FFXV, I was sold on a next-gen. Even though I'm a Sony player, I tried to keep an open mind going into E3, but after looking at everything I thought (as well as most of my friends) that PS4 was clearly better. Apparently Microsoft agreed, since they are backing off a lot of their negatives.
Honestly, apart from KI, Halo, Gears of War, and Fable, I don't know of many xbox exclusives. I am interested in Gears of War. Yet, a list of the Sony exclusives have already been listed, and many of them like God of War and Uncharted are outstanding. The God of War series is one of the best all-time game series, and Uncharted is amazing. I think Uncharted 2 is one of the great all-time games.
A couple exclusives for Sony that I haven't seen mentioned are Team Ico and DUST. Team Ico only makes a game every few years, but when they do it is top-notch. Shadow of the Colossus is one of the greatest video games ever. They make Sony exclusives. DUST is the first console game to ever link up with a PC MMO, in this case EVE Online. That is historic. No one has ever done that before. My buddies and I can play our FPS DUST on the console while EVE players are coordinating air strikes for us from their PC. That is super cool. They tried to include xbox initially, but didn't get cooperation from Microsoft, so bailed on it for xbox.
To me the best argument for xbox 360 over a PS3 is just that so many people have 360s in America. If going forward XB1 loses any traction to PS4, it only decreases the best argument for XB1, and a $100 price difference might just do it.