War is hell
Sometimes, you're just in the mood for something brutal. Something with a learning curve that arcs up to kick you in the face. Panzer Tactics DS has just what you need on those occasions.
This full-featured strategy juggernaut has a lot going for it: the ever-popular WWII setting, loads of missions, and a great single player experience. Multiplayer, outside of local multi-card, is somewhat less than good, but hey -- you've already got Advance Wars for multiplayer. Panzer Tactics can fill all those other hours.