Darius changes are a pretty big nerf to jungle Darius.

Literally every aspect is worse now. I literally just bought him, and being a jungle main decided to try it out, and I loved it. But the new changes do hinder it a bit.

Base Stats: Less attack speed means slower applying of passive and overall slower clear, although the extra AD should counter that.

Passive - Hemorrhage: Bleed does less base damage and doesn't scale as well, so less damage on one of his best clear tools. Also, based on the wording in patch notes, I guess the 5 stack bonus only applies to champions, although if it did apply towards large jungle monsters by any chance, his clear would be much better. Also, taking the movespeed away makes his ganks a little worse, but I think a Flash E into his new W will make up for it.

Q - Decimate: So god damn bad early game... Seriously, I don't think changing the scaling to total AD instead of bonus is going to do much, since Darius can't really afford to not buy tank items. And it'd be fine if his heal at least applied to large jungle minions, but of course season 5 was all about jungle diversity so why would they let another champion jungle?

W - Crippling Strike: With the attack speed slow gone, there goes the tiny amount of sustain Darius had; slowing a jungle creep's attack speed. And the cooldown reduction removal removes a huge clear tool Darius had since now he can't constantly W for damage. One the bright side, his slow is kinda better, if you consider that the slow itself is now more than twice the slow, but half the duration. However, don't forget there is a hard cap on how slow you can go, so they still won't drop below that. Overall not too heavy of nerfs, but his clears and sustain are hurt, luckily his ganks are somewhat buffed, which is what he excels at in the jungle.

E - Apprehend: Actually a pretty good change. Riot removed a bug, and also made it so champions can't escape after getting apprehended. Overall I'd say this change definitely helps, since his ganks will be more powerful, and his E isn't used for farming the jungle.

R - Noxian Guillotine: Lower damage makes me sad, but at least now in fights his new passive basically snowballs him in the middle of a fight, and I feel like this could actually make him a decent 2v1 fighter, or even be able to be assassin-like since the damage bonus would mean the enemy would get destroyed after you kill one person.

Overall I wouldn't say these changes are going to completely gut him in the jungle. On the bright side he doesn't need to max his W for CC anymore, and overall he kinda has more damage. And the changes promote my personal style of saying fuck it and building full AD. With a little bit of movespeed and attack speed runes/masteries, he should be able to actually gank better now since he can just get his 5 stacks and destroy someone. And now he has some nice CC. The only major drawbacks are his only sustain (W attack speed slow) is now gone and his base damage on Q is lowered and W doesn't scale up as hard. But, Riot does kinda promote building Darius extra damage-y and focusing on going for dunks and chaining them together in a fight.

Honestly, if his Q heal also applied to large monsters, I think he'd be perfectly viable, although I'm not sure Riot necessary wants Darius to be more than a top laner.