You got me!
Obviously there are a handful of issues with NCAA 10 that I find personally annoying. Others may have no issue with them.
1) The new camera is problem #1 for me. For those that like the new camera this obviously carries little weight and would give NCAA 10 more love. But for those that hate it, it really hurts the fun factor.
2) Pass speeds are way too fast. This makes trying to play pass defense impossible for me and led to a lot of frustration by the end of my rental with it. For those that play only as a defensive lineman, this probably doesn't bother you at all.
3) NCAA 10 is much better out of the box than 09. If you don't like to play with sliders and/or like to play online I'm sure this is a big plus for 10. But I only play offline and I tweaked the sliders like crazy in 09. Yes the sliders work a LOT better in 10 but I was able to come up with something that ended up working pretty well in 09 on Heisman. AA is a much better difficulty level in 10 - I have no problem saying that as AA in 09 ended up being pretty crappy. The cpu QBs aren't nearly as stupid in 10 either although the hit the QB - DT INT issue is a problem in 10.
4) I disagree with those that say defense didn't exist in 09. With slider tweaks and my skill set, I have no problem getting good defense from both me and the cpu. Maybe I suck but I just don't agree with those that say defense was non-existent in 09 (at least a heavily adjusted 09). For some of the truly great players, it may be true. But for me, this is not an issue.
5) Pursuit angles. These were bad in 09 but some people act as though you saw something stupid every play. I'd see a bad example once or twice a game. Again, my sliders and my skill level. A far bigger problem in 09 was the greased pig animation where a defender would fall down when trying to make the tackle. That did suck but I still saw a form of that in 10 - just that the defender would whiff badly without falling down.
I do really like the fact that the cpu goes deep in 10, over the shoulder catches are sweet, the cpu running game and sliders are MUCH better this year, and the break out of the tackle thing is neat as well. But for me, the flaws I do see really hurt my enjoyment of this game to where 09 is more enjoyable. Give me my old camera back and slow down those crazy fast passes and I'd probably make the switch. Until then I won't do it.