For me improvements and additions over FIFA 08:
No more rails please, either add in some sort of "super cancel" or just give us total player freedom of movement.
Too many times you pass to someone and he just stands there whilst an AI opponent nips in and pisses off with it.
Get rid of the bs stat levelling on the higher difficulty levels.
Dribbling needs to be a tiny bit more respsonive to feel realistic.
Better and 100% more responsive player switching after corners, or just being able to sometimes would be a start.
On pitch refs & assistants.
Your AI team mates, ffs stop them just wandering into you whilst you're dribbling. So many times they've just wandered infront and "tackled" me whilst getting into a shooting position with a midfielder.
The advantage ruling, they need to do what PES has and give delayed cards out rather than forget about them once the advantage has passed.
Create a team/franchise if its do-able.
Starting with creating a kit, building a stadium then getting a team together etc...
Build on the be a pro mode by having a career option where you use your created character.
Freekick system.
Give a little more depth on these.
Trance_Allstar usually has some excellent ideas on free kick setups in these threads if i remember rightly.
Something like adjusting your run-up, having a golf sim-esque ball where you're going to strike it then holding the button for the desired power.
Using the driven shot, finesse shot and shipped shot modifiers whilst the bar is on as per normal.
Nets.
Totally non important really and more of a nice to look at thing. But they need to be a tiny bit saggier and ripple more.
Also more variety such as ones with a horseshoe like stancion in the top corners although i'm guessing good net physics for those would be a lot harder than the box style, could be tied in with the stadium creation in the build a team idea.
More crowd chants, on pitch and pitchside voices.
More stadiums.
A training mode.
Include being the keeper in be a pro.
Weather be it dynamic or set, there should be rain/snow/wind etc...
Pitch wear and tear.
Better comentary scripts.
Better options for player creation, more hairstyles, boots, goal celebrations etc...