They advertise an average of 6 Young Guns cards per box and that's been consistent for me.
You'll net 2-3 Jersey cards, 2-3 Hockey Heroes, 3-4 Canvas cards and the odd Young Guns Canvas Card.
Series 1 has EA Ultimate Team and All World cards but they're nothing special
Series 2 has stuff from O-Pee-Chee, Victory and MVP cards. I like the MVP Rookie cards so its thankfully not pure filler. You can get more than the standard 8 cards in some packs because the OPC stuff is on a thinner lower quality stock. On the other hand, if you get a patch like the above, you'll only get 2 other standard cards in the pack.
I've pulled 1 UD Exclusive parallel card (numbered out of 100) per two hobby boxes; 1 from S1 1 from S2. Got none from either of the two retail boxes I grabbed off eBay.
Stuff I've not pulled from 6 boxes are Clear Cuts, Signature Sensations and Spectrum parallels (out of 10).
Check out these two links for a review of each series, there's some photos of each card type: