I love writing video games for fun, and often do that.
I noticed, anyway, that most of the times implementing the gameplay itself doesn't take too much time to me (maybe because I already did that plenty times and know what and how to do for most of the things), but when I try to implement off-game stuff I get lost.
By off-game I mean what is not gameplay: menus, cutscenes between levels, world map to choose levels, saving and loading status, managing replays ... Only tried to write a few of these a few times, but always failed; that's why I never really completed and distributed a game.
Are these common problems? And where should I start to do this? Where could I find some books/guides about such stuff?