Best Flying game since Crimson Skies
Local multiplayer is great 2 person split screen, and you can add bots for a total of 16 players.
Xbox live is the same but without bots, 16 people flying around and causing havoc.
A bonus awesomeness is the kill streak awards, at 4 kills you get woodstock covering your tail, and at 10 kills you get to fly Snoopy's Dog house.
Bottom line is if you like the Peanuts, and/or like Crimson Skies, get this game you won't be disappointed.
9.5/10 only because it isn't 4 person split screen.
UPDATE
Just played through the single player, here is my little review. It's fun. But there really isn't a storyline, I mean there is a vague Red Baron evil scheme going on. But the game plays like just a handful of mini games stretched out over a variety of maps.
Not to say this is a bad thing. It works, the mini games are fun and challenging, you can customize your plane before any mission. Gives the game a lighthearted childish nature that really plays into the Peanuts.
Multiplayer is the heart of this game, the single player is just the icing on the cake. A must buy.