Not an expert on gryphons but the tail might be too short if you based it on a lion's one. As always you managed to get the general shapes and forms on the first try, congrats! Just, the back looks too rigid: it could be a bit more curve between the hip and the shoulder (just a bit though).
As for the head: the neck looks pretty short and low, and the head a bit too "compressed", as if it was lowered in height and stretched to the side with the selection tool. Could be me though.

Keep practicing!

Thanks for your help.
I agree on those errors, the neck is actually not existent... I have to fix that and everything else :P

"Keep practicing!", I will.

Only thing that stands out to me is the shape of the deltoid/triceps/biceps. Cats generally don't have a whole lot of muscle definition. Well, they'll have creases, but not so much bulges. Depends on the refs, tho.

I don't think the lower back needs any curve... cats spines are actually pretty straight across. Their shoulders typically create a hunch that makes the spine look like it curves, when it doesn't really. Which is exactly how it looks in this pic.

As has been mentioned before: very nice sense of form and volume.

Love the attitude in that expression. Someone knows they're king of the beasts and sky. X3

Bestest guide to drawing wings I know of... second half of this: http://majnouna.deviantart.com/art/Drawing-Birds-part-1-22106533?q=gallery%3AMajnouna%2F6557&qo=14

Anyway: Hope this helps some.

Thank you for the feedback, fave and the tutorial link, will be very useful :)
It helps a lot :3

Anytime. X3 Majnouna has a lot of useful tutorials.

Looking forward to seeing how this develops. X3