Kerbal Space Program

It's really nice that you can do multiple speed/altitude contracts in the same mission, but it would be really nice if the planet/moon exploration missions followed the same pattern, so that you don't have to bounce back and forth between the flight and mission control so much. It would also have the benefit of letting players choose which planet or moon they explore next, so if you want to do minmus before mun, you won't have to give up those contracts. Same for out of order planet exploration.

If you want the cash advances to still be available(though I think it's probably unnecessary), you can let the player accept a contract one step beyond the automatically assigned contracts. So after orbiting kerbin, you get an automatic contract to flyby mun(reward only), and the option to accept an orbit mun contract, with part of it's reward given in advance.