20. Advance Wars (2001)
Dropping from 15th over the last couple years, is the game that actually prompted me to get a GBA. This was pretty much the classic war-type board game brought into the video game world. In other ways it was so much better. The results of individual fights were usually pretty predictable so you could strategically plan multiple moves ahead without needing to have too many contingency plans. The gameplay is fairly simplistic, build, move, attack, capture and there's often multiple ways to win. Add in a campaign which ramps the difficulty almost perfectly and its hard to get too discouraged playing this game. The CO powers give you an advantage for a short time so you have to be careful when you use them and your COs base specialty actually has an impact on what units you build. Fog of war and varying victory conditions added almost as much extra gameplay as the large set of maps already built into the campaign and war room. Overall this game shines because it really feels like you can do well no matter who your CO is and the balance of the individual units on top of that works nicely.
Primarily an RPG player but have interest in any game that will make me think.