It's not that great.
Madballs in Babo: Invasion
Pros-
#1. Decent Graphics
#2. It's cheap to buy
#3.You can use several guns
#4.Multiplayer
Cons-
#1.It's boring after a few minutes
#2.It's not even close to as fun as a real FPS such as Team Fortress 2
#3.It's not even close to as fun as playing with marbles in real life
#4.Most old school action games are way more fun then this
The Bottom Line -
I would not call it a shooter at all.That is like saying when Mario from Super Mario can shoot fire balls then that is a shooter.That is like calling Mega Man a shooter.
I was never that into old school action games.I could play them for 15 minutes but then I would get bored.This game is just like that for me.
If you can play old school action games for hours then this game is for you.If you can't then this game is going to get really boring really fast.
My 2 cents
Dan