Full disclosure- I'm an OSU fan so while I may have paid more attention to certain things than a non-fan, I also come with a bias..A lot of things occurred in the OSU game to explain the tale of two halfs.
Certainly the passing game in the first half by IU was outstanding. The taller bigger receivers had an advantage on some of the jump balls. If you look at some of the catches with tight coverage there were some incredible efforts that while highlight worthy, were unlikely to be duplicated over and over with consistency. The OSU DBs had three new starters and they played like it in the first half, but adjustments and improved performance in the second half showed the potential. While there were a lot of complete passes, none broke free for big yardage or a long score which is a testament to the Buckeye speed on defense.
Offensively, Barrett is not a classic drop back QB and if they continue to try to make him one it's a mistake. Since he was a freshman, Barrett is a very good passer but he needs to mix it with his run game. I compare it to a boxer who needs to get hit a few times to get going. Barrett seems to get better when he's had a bit of contact. He just shouldn't be carrying the ball 20+ times which he tended to do last season. He is also a rhythm QB so he needs to be able to be given the chance to get into rhythm.
This was Indiana's Championship Game. They had ESPN Gameday there, they had a new coach and were going against their old coach. This was supposed to be their coming out party. This was the game they prepared all off season to give their best shot, and they did, While it was important for OSU, a week and a half later they have Oklahoma at home. If the Buckeye coaching staff was implementing any special game plan or practices for an early game during the Spring, Summer, and Fall Camps, it's likely they were preparing for the Sooners, not the Hoosiers.
In some ways it ended up being a great situation for the OSU coaches. A good win where they Saw how the team responded under duress. It was against a decent team and was able to see where some weaknesses were, and can be addressed, that wouldn't have shown up against a lesser non-conference foe. Now they have nine days to work on it.