The Gameboy Advance may be limited but with great gameplay mechanics and functional graphics, Advance Wars is up there with the best games on the system. It is a turn-based strategy on a grid, with similarities to the same developer's Fire Emblem series.
In the main campaign, most of the missions involve a fixed set of units, but some missions allow you to create more by spending money that you accumulate each turn. You win by wiping out all units or capturing the Headquarters.
There's land, air and sea units but not all are available on each mission. At first, you just have the land units to get used the mechanics. For the land units, there's Infantry, Mech (infantry with rocket launchers), Recon, Small Tank, Large Tank, APC, Anti-Air, Artillery, Rockets, and Missiles.
Infantry can capture buildings but are only really good against other infantry. Mechs do more damage to tanks but are still inherently weak because they are still infantry. Recons are basically weak vehicles which are strong against infantry but weak against tanks but have really high movement range and visibility (on maps with Fog of War). Small tanks are good against infantry, and all vehicles except the Medium Tank. APCs transport infantry and also refuel and resupply adjacent units. Anti-Air are very effective against air units but also effective against Infantry. Artillery, Rockets, and Missiles are ranged units; they have a minimum and maximum range and deal high damage. Artillery and Rockets attack ground (or sea) units, whereas Missiles are specifically anti-air.
The Air units have great movement range and are effective against land units except direct anti-air units. Fighters specifically can only attack (and are very strong against) other Air units. Air units still block ground unit's movement which is a bit illogical. The Sea units can only move on water, and you have: the ranged Battleship; the stealthy Submarine that is effective against Battleships and Transport ships; and the anti-air and anti-Submarine Cruiser.
Ground Units cannot move when they run out of fuel. Air and sea units crash and are destroyed. Ground units gain bonuses from the terrain. The terrain's defence bonus are river and roads (0), grass (1), forest (2), city (3) mountain (4). There's different movement ranges for each unit, and certain restrictions. Air and infantry can go over mountains or rivers, but land vehicles cannot.
When attacking, the aggressor has the advantage - so if an Infantry attacks Infantry, the defending unit will end up with fewer health points. It's basically the aggressor deals damage, then the remaining defenders will attack back. If you strongly overpower a unit then you will take no damage at all. Only direct fire units can counter direct fire units, so attacking with or against a ranged unit won't encounter a counter-attack.
There's Fog of War on some missions, so you need to proceed carefully to uncover units before you can attack them. Your land units can hide in forests, and ships can hide in coral.
The armies are Orange Star, Green Earth, Blue Moon, Yellow Comet and Black Hole. In the Campaign missions, you play as the Orange Star army. Their Commanding Officers (COs) are Andy, Max, and Sami which are introduced during the first several missions. You can choose a CO to play each mission and each one has a different CO Power and traits. Outside the campaign, you can unlock CO's from the other armies to play single missions with.
Andy is a balanced character and his CO power heals 2 health points which I found very useful. Max has stronger direct attack units, but loses 1 range which makes ranged units almost useless. Sami has weak mechs but infantry are stronger and have 1.5 capture rate, with transport units having 1 more range. She is useful on certain missions but generally seems a harder character to use.
Some of the enemies seem a bit overpowered with their CO powers. Grit has 1 extra range by default which makes him tricky to play against especially when his power gains an extra 1 range which is brutal. Eagle's power allows him to take an extra turn which is obviously a huge advantage. Drake damages all your units by 1 which is a massive inconvenience but if you use Andy, he is good to use against Drake to cancel that out. The final mission is really hard due to the CO having an area of effect attack in a 3x3 grid that deals 8 damage. When you feel like you are gaining an advantage, it's usually time for his power which is brutal when he drops it on a few expensive units. I did think the game was slightly easy at times, but these powers do increase the difficulty when used.
The story is a bit silly. A clone of Andy has been battling nearby regions to start a war between all these countries. Even when these armies realise a fake Andy has instigated a war, they carry on fighting as "a test" or "a distraction". Not really realistic - unnecessarily sacrificing many people's lives, although you can say the distraction tactic was for the greater good.
When you are playing a mission where you can create more units, it is vital to capture buildings where you can create units (base, airport, dock) and defend them to gain an advantage. Income is generated by how many buildings you own, so you need to take cities from your opponent to weaken them. You can repair units at captured cities or bases which is another advantage.
The battle animations will get old at some point but you can turn them off. There's a few options too so you can just have them on when you attack if you wanted.
One slight flaw in the game is that there's a First player advantage. On some missions, you can take down powerful units on the first turn. They may be intentionally placed close to you as part of a story - you destroy nearby units then take the fight to the enemy.
On some missions, the AI seems intentionally nerfed, like he has a tank but wont move it until you come in range, even though taking the initiative and attacking would be extremely beneficial. APC and transports seem high priority for them to attack, so sometimes you can sacrifice these units and sneak some tanks through to deal damage next turn. I also think the AI struggles in certain scenarios, particularly the larger maps that you unlock outside the Campaign.
Even though there's a few flaws, I think Advance Wars is a brilliant turn-based strategy with well-designed units and mechanics. I still remember playing Advance Wars 2 a lot, so I went into this game with knowledge of the mechanics and strategy. Newer or younger players will find the game much more challenging.