In this context, "wicked" just means "very good."
The Googly is a delivery from a type of bowler called a "leg spinner" - he bowls the ball and it lands, or "pitches" on a line with leg stump and then spins toward off stump.
Like this :

After facing several, (maybe even tens), of these types of deliveries the bowler will slip in a "Googly" or, for those upside down people, a "wrong 'un" which is a ball that goes the other way.
So you get used to the ball pitching on your left (if you're a right hander), then jagging across you, trying to entice you into getting the edge of your bat on the ball, so you can be caught out. Then suddenly you get one that looks like the bowler has got the line wrong, because it's going to pitch further to your right, you react to it as if it's going to jag right and hello! It jags left and you're in the wrong place - if the ball hits your legs you can be out "LBW" because you stopped the ball from hitting your wicket with your legs.
Essentially, a lot of the danger of the Googly is similar to the change-up in baseball - it's dangerous because of what it's not, as well as what it is. In baseball you misidentify the change up as a fastball and you're through your swing too soon. In cricket you misidentify the Googly as a standard leg break and you move to the wrong place.
Best. Comment. Ever.
If you're interested further, here's a couple of videos :
Leg Spin Basics
Shane Warne's Five Leg Spin Deliveries (The Leg Break, the Googly, the Flipper, the Slider and the Top Spinner)