Extreme, fast-paced flying, shooting action!
The game is pretty short too. There's only so many tournaments and challenges. It's definitely not made for multiplayer. You could have a dogfight with 7 friends, but the chances of having 7 friends who won PSPs available on the same day is rare, let alone 7 people who all own a copy of the game. If the off chance that you have 7 friendly PSP owners nearby, but they don't all own the game, you can play, but are limited to a single track and a single plane.
The game is great fun, and provides lots of action, but is lacking in variety. It's too short and repetitive. Still, I enjoyed playing it, even though I was able to complete every tournament and challenge in about 3 days. I'd still try out a sequel, hoping it will be a bit longer and have more tracks, planes, upgrades, and weapons.
I would recommend M.A.C.H. for gamers new to the flying genre, but if you enjoy playing Microsoft Flight Simulator on your computer too much, don't quit for this.