The only thing I'd like to see improved for DmC, is the JC'ing. I only recently started playing around with it... and I went back to DMC3 to see how it was. I have to say, I love that it's become about timing rather than positioning. The only enemy I enjoyed jc'ing on were the bloody demons Vergil fights in the opening cutscene. They were super easy to cancel on, and it was really satisfying bringing them into the air and cancel vergil's first Yamato slash.
In DmC, something feels off about the JC'ing. Cancelling rebellion/arbiters 'Circle' attack just looks ugly, and I don't really like doing that... but Osiris's first areal slash looks nice to cancel on, actually both angel weapons look nice to cancel with... but even with those, it just doesn't feel as satisfying as Vergil's Yamato. Maybe it's just the speed of DMC3's slashes that made it more satisfying...
One thing I would hate to see, is JC'ing to go back to how it was in DMC3... It's just too difficult to cancel on almost all the enemies. There's a reason I never bothered with it until I started to get bored with DmC. I'd like to see more air attacks, because with DmC the main two things I ever cancel is Calibur and the first slash to Osiris. I sometimes cancel Rebellion's first slash, but it doesn't look as nice. I mainly like to go Osiris- Slash, cancel, Slash, cancel, Slash, Slash, pause, Rebelllion- Slash. Or... I just spam Calibur.
Other than that... I want to see a toggle-able lock-on, more attacks, customization to devil trigger, and more perks. There's a huge list of things they could have done with perks... since HoH has no unlocks, they could have added perks upon completion to make the game harder (Remove enemy weaknesses/stuns for example).
I could imagine the perk menu being like Goldeneye's (3:08),
More perks could be amazing to have. I'd love to tweak Dante to my personal preference, such as racking up devil trigger as quickly as previous DMC's, and using it up as slowly as them too. I would have also loved to disable the DT fog, and disable the ability for it to launch enemies into the air. Heck, I would have loved a 'Super Guns' cheat too, to really boost up the damage that guns deal.
EDIT: I meant to post this in another thread... just in case your wondering why its so off topic. :/