Better commentary (probably gonna be one of the most requested at a guess)
Also have the commentary track the season and recall major events.
Perhaps establish rivalries between players and clubs.
Better crowd chants and noise, a little more emotion rather than the dull cheer when you score.
Better celebrations + celebrations that are appropriate to the moment (scoring the go-ahead goal in the last 5mins your guys should go crazy)
Have more call names in the editing area.
Keep improving the kit editor.
Better choice of balls & boots.
More teams & more of them licensed
Longer replays, i'd like to see the build-up play, not just the last pass then finish.
Also the replay option not ghosting out after the ball leaves the field.
Show other important game's goals at half and full time from in your league.
Pitch conditions effecting players more.
e.g - really shitty, muddy coniditions causing guys with lower balance to slip and fall more.
Better net physics, like those in Football Kings, more sag and billow to them.
Also a choice of net styles (box net, horse shoe in the top corner stanchion etc...), colours, hexagons or squares etc... (could go well with creating a stadium).
On the creating a stadium, could have the normal stadia which are already in the game, then leave about 2-5 blank slots for your own created stadiums.
A penalty taking system that isn't so random as to whether it wants to go on target or not.
Maybe incorporate the power bar and/or analogue control of aiming?
Obviously better skilled players would be more accurate as to where you're aiming.
Its a pet hate of mine when i played football, but diving could be an interesting introduction if done right.
They'd have to work it well though so it isn't a money move as then we'd have 22 Joe Cole's on the pitch.
Scenarios.
The ability to take a quick free kick, throw-in or corner.
Fun stuff like 5-a-side, knockout, beach football (unlockable)
Linesmen
Coach/Manager
Bench players warming up
Female streakers