As others have said, a balance.
I don't want it to be as hard as 08 is. 07 was pretty easy, or maybe I just had a knack of creating great tactics. I'd like a fun game. Hell, if it was fun I'd love it. However, I don't want a game where you can take Bishop's Stroford to the quadruple in 6 seasons with a basic 4-4-2.
If you play Man U and you are a mid table side, there are 3 ways you can realisitcally come away with anything:
1. Play 4-5-1 or 5-4-1, not giving them space and man marking
2. Be extremely lucky
3. Be Spurs!
I'd like it to be that way in the game.
There is no way winning everything would be any fun. If you want to live out fantasies, don't play FIFA Manager, it sucks, just imagine.
Tactics are important (that's why your PE teacher kept going on about them when you were playing badmington

), but if you put out a team that is far superior (say, 4 divisions), you'd have to be using an awful tacic (i.e. 2-3-5 with wingers.) If you play a team that is one division below and only slightly inferior, you'd have to play a reltively sensible formation with decent instructions. If you play a superior team, you'd have to use a good tactic but not the perfect ones you have to use at the moment. In any situation, however, there should still be a small chance that it wouldn't pay off (and that goes both ways, for the AI and the manager).
FM07 was pretty realistic, and very, very fun, but 08 is neither. SI are trying really hard, it's plain to see, but they've made a few mistakes, such as the two year plan bug. I belive that any game should be realistic, but only to the extent that you shouldn't be able to buy VDV in the Championship.