Absolutely IMPOSSIBLE!
I'll outline the good points and the bad points:
Good Points:
Easy Gamerscore
Funny Jumper Special Kill Cutscenes
Now the Bad:
Terrible Fixed Camera
Utterly Impossible
Too short
Can't dodge to save your life
Too many enemies
Undodgeable enemies
All you do is button mash
Some enemies are unkillable
One boss keeps tapping you and you die
Its really easy to die
Can't dodge really slow projectiles
and the list goes on. This is by far the worst game I have ever played, it beats skate. by a million points! I gave skate. a 5 for being too frustrating but it had some comedic relief since every time you bail, you get a realistic impression of what it might look like in real life!
So my score of Jumper: Griffins Story, since I can't can't go lower than 1 on Gamespot:
-10,000,000 / 10
Unplayable
Go dump this game next to E.T!