Q went from bonus AD to total AD.
Level 1, hitting someone with the blade on live does 105 damage.
Level 1 on new Darius, hitting someone with the blade will do 156.
The scaling also goes up in rank for the new Q.
Level 9, lets say current Darius has a Ravenous Hydra and that New Darius has a Titanic Hydra. THats 70 Bonus AD on Ravenous, 50 for Titanic. New Darius has 96 Base AD at level 9, putting him at 166AD.
That means his Q, now rank 5 will do as follows while hitting the blade:
Live Darius: 388.5
New Darius: 304.4
New Darius with Bloodrage: 430.4
Level 18, with a Ravenous BC for current Darius, Titanic BC for New Darius.
Base AD for new Darius at level 18 is 141, with 90 bonus AD for 231AD.
Live Darius: 430.5
New Darius: 423.4
New Darius with Bloodrage: 703.4
Things to consider for New Darius:
Bleed applies cleaver stacks
Titanic Hydra's active can be used to stack passive
Titanic Hydra's active does much more damage than Hydra's
Can gain a 40(lvl1), 70(lvl9), 200(lvl18) AD steroid (40-200 depending on level)
Slower
Less attackspeed, but with more auto-attack resets(ravenous is not an AA reset, its an AA cancel)
Q heals Darius for 10-30% missing HP per champion hit.
Apprehend max second makes him more effective against tankier targets
Things to consider for Old Darius.
Faster
No Delay on Q
Lifesteal on item
All-in-all, Darius is stronger early, weaker mid game, equal to insanely stronger late game.
Also remember that you will always have bloodrage for your ultimate if you ult at 5 stacks, adding a minimum of 300 damage to Darius ult at level 18, guaranteeing 900 minimum true damage per bloodrage dunk.