The Advance Wars series (GBA, NDS) have always been a favorite of mine and have provided entertainment on long car trips. There are 4 games in the series that I can think of off the top of my head:
Advance Wars (GBA)
Advance Wars: Black Hole Rising (GBA)
Advance Wars: Duel Strike (NDS)
Advance Wars: Days of Ruin (NDS)
(Old GBA one, either the first game or Black Hole Rising)
(Days of Ruin, the most recent in the series)
Game play is turn-based. On one player's turn, they can move units and attack with them, and produce more units with certain buildings.
There are 2 or more "nations" on a map. Each nation can (usually) capture cities to maintain their economy and factories to pump out soldiers and war machines. Winning a battle results in one nation's "HQ," or headquarters, being captured, or having their army completely obliterated.
Maps are made up of different terrain tiles that do different things. Cities and factories, as said earlier, provide funds and produce units. Special "factories," like Ports and Airports can create ships and aircraft. Terrain tiles such as "Plains," "Road." and "Mountain" provide different movement restrictions and defense stats.
The AI is superb in all of the series, you can easily be out-smarted and destroyed if you make a wrong move. It can get pretty frustrating in some campaign missions where you're at a slight disadvantage in the begining and the AI starts with a massive army, and you have to go through the mission several times before you succeed. Come-backs are near impossible, if you've lost a major battle and a large amount of buildings, defeat is only a few turns away.
All of the games also have built-in map editors and multiplayer. You can battle with your friends or trade custom maps.
