Ryze's skill floor went a lot lower. You had one combo, and had to execute that one combo to perfection in order to actually do anything with old Ryze, while with new Ryze the combos are a lot easier to perform due to not having a specific window to do it, giving players a lot larger understanding of what combos you can do, and being able to switch combos when you end up messing one combo up.
From my experience playing both old Ryze and new Ryze, that was basically the case. I couldn't do Ryze's old combo to save my life after trying to learn him for 3-4 games, but I can do new Ryze's combos pretty easily after 1-2 games.
The only thing that's really much harder about new Ryze is his ultimate, which is really hard to use well. I don't think I ever used it for a good engage at all until I had around 3-4 games on him, and literally only used it to escape ganks until I found some really good opportunities to use it in the most recent games I had on him. It takes a master to use it to its full potential, but you don't need to be a master to use it.