He's harder to learn than Akira as far as a neutral game; mixups, pressure, opening up your opponent, etc. However, Akira still takes the cake as far as execution. Jacky isn't all that difficult in that aspect. What is difficult is how you have to consciously be aware of all his options 24/7. So he's hard to pick due to his endless options, but his combos are pretty simplistic.
Incognito summed it up great. All of his executions are actually very easy save the kick recovery cancel. But he has so many options that "mastering" him takes some time getting used to all he can do (like Leifang). But, the learning curve isn't as sharp as Akira because you will be more comfortable and capable from the get-go.
Hard? Maybe he's a little easy to me because I'm already accustomed to his VF counterpart. But the only hard thing about him is properly utilizing his 6K:G. His damage comes off as ass at first but it adds especially if you're counter hit frame trapping which jack does well.