This is exactly what the series needed: new and restructured units that allows for more focus on your tactics and meta game, revamped CO system, more streamlined gameplay, and Wi-Fi battles over the internet.
The Campaign starts off fairly easy if your an Advance Wars vet but quickly ramps up in difficulty that provides enough challenge, but really it just seems to be a long and drawn out tutorial that prepares you for online battles. There is a lot more story and dialog behind it, but is a more realistic affair than previous outings and more to my liking.
The new CO system is great and serves to think better about the influence your CO has over the game. Just don't forget to add him/her to one of your current units, which I have done so a few times even realising half-way in some skirmishes.
Some may complain about the absence of modes like the War Room, Shop and Survival modes, but for me the shop was more of a gimmick (apart from Hachi's wisecracks) and the Survival and Combat modes just took attention away from the main game.
Also with the Map center that allows you to download maps from other users online along with uploading one of your own you made in the Map editor (with restrictions), you shouldn't have a reason to complain about new maps.
A must buy!!!