If i was being realistic about what could be achieved and also wanted it on the market, it would be this:
An RPG game which isn't too realistic, but not too ridiculous, has an excellent script and storyline, and love-able characters. A WIDE variety of things to do within a massive (but not stupidly massive) world. I would love complete character customisation, but it's always done appallingly, so if i'm being serious, i'd rather not. A proper linear storyline but on a monster scale. Essentially a fighting game, but with loads of options how you go about it, and then heavily stressing on other puzzles to push you through the game. A few fantastic settings, comprising of diverse-looking towns, villages, cities, countryside.
Ahh, 'twould be amazing.