Those other wars
What's that? Advance Wars: Days of Ruin is the first Advance Wars game you've played? Boy do we have a treat for you! Not only is there Advance Wars: Dual Strike, which is widely regarded as the pinnacle of DS strategy (and some still think so, despite johnny-come-lately Days of Ruin), but there are GBA titles in the franchise as well. If you missed any of these, you might want to start there rather than with any of the other games in this list; after all, you already know you like Advance Wars!