I haven't played Fable 3, nor have I finished Fable 2, but from what I can glean from it, 3 was the absolute worst of the series. So...
Lesse...
1) More open-world areas. Think Fable 2's maps, only larger.
2) Fable 1's combat. It wasn't perfect, but it was a lot better than whatever Fable 2 was supposed to be.
3) Difficulty. Either you reduce the health potions, you reduce the food, you reduce the damage we deal, or you increase the health and damage enemies deal. I died in Fable 1 once in that Hobbe Killing Contest, and that's just because I was having a bad day with those mage Hobbes and the explosive barrels.
4) A better story, or at the very least, something up to Fable 1's level of coherency. At least in Fable 1, I knew what the fuck was going on.
5) Boss battles are supposed to be difficult. WHY AREN'T THEY DIFFICULT?
6) Expression wheel from Fable 2. Also, it's a bad sign when that was one of the most enjoyable parts of the game.
7) FOR THE LOVE OF GOD, MOLYNEUX. STOP DROWNING US IN MONEY.