the things i'd like to see improved:
kits - i don't like the fact you cannot change your kit at least once every two years, it is unrealistic, it is a pretty easy feature to enable, all you need to do is maybe ask the board for a kit change, if they grant it you could change the kit like you choose a kit on a fantasy league e.g click on the sleeves on the shirt to change them
stadiums - sometimes you go to lower league teams and there stadium is massive compared to the size of their club, they should be a bit more realistic and research each ground thoroughly to see its features, at least for english clubs anyway, also it is unrealistic when lets say you go to old trafford and the away support is filling the whole of the stretford end, the main stand at old trafford
stadium expansion - i think the board should consult you about expansion and what you'd like to expand, like they did in LMA manager years back, you can choose how many tiers the stand will be, where the main stand is and where the away supporters will sit, the name of each stand, the exact capacity of it (obviously you can't put in ridiculous numbers and work your capacity to a budget e.g. if you are wrexham you can only have a maximum capacity of 20,000 because you can't afford any higher) also you could build the stands like you build a rollercoaster on rollercoaster tycoon
other jobs in game - maybe after you retire you could become a chairman which means you hire and sack the manager, build a new training ground/stadium, look after the financial and commerical side of the club and give the manager his transfer budget for every season, or you could become an agent, have several players as clients and manage their contracts, discuss terms with clubs and advise players, get involved in rows with managers and trash talk and talk about your client to get clubs interested, or you could do what some old managers do when they retire, take up scouting or become a consultant/director of football to a younger manager, when you start out in the game you could be an assistant manager and work your way up the managerial ladder from there
better transfer dealings - i think the current transfer system is good and has worked for years now but you could tweak it a bit, become more involved with players agents, have a transfer saga, intergrate newspaper rumours, meet with the interested player, promise him the club will buy him a house/car etc like in real life, agree terms with a player before you agree a fee with clubs which happens a lot now
relationships with clubs - i think some clubs are very hard to please, e.g. i was manager of millwall for two years, got back to back promotions with them and won the FA and league cups then resigned to manage man united, in real life i'd be regarded as a legend at millwall, but i'm not even on favoured personnel on the club information screen, its unrealistic
more retired players/managers available - maybe they could make more retired players available to be tempt back into coaching e.g. alan hansen even though he has never coached after retiring be available to take the assistant managers job at liverpool, that happens occasionally in real football, also maybe older managers coming back to become an assistant at a favoured club (ferguson, harry redknapp, george graham etc), even though some old managers are available to become coaches they never accept e.g. terry venables even though he is getting no offers to become a manager anymore will never accept a job at old and favoured club tottenham even though the option is available
rant over, i know that not all of these things will happen but its just ideas