The big hard important things are highest priority to get done. However, that doesn't always mean that they should be first on the to-do list. For the simple fact of motivation, it is better to mix in small, easy projects with the bigger ones, and fixing bugs with adding new features. Heads down work on the hard systems is taxing on the programmer and it provides very few rewarding moments - it's a big work towards releasing anything and it looks to players as though nothing is getting done until the big release. Not that it's bad to do those too, but little fun things are fun to program, they're quick and easy and revitalizing. And when people get to go 'Ooh! New stuff!' that's revitalizing too. So a mixture of projects keeps the programmer working at his best for the ones that are 'highest priority'.
Temi