I find Ryze to be a particularly interesting character in the league in that you only really see him played at the extremely low ELO's where he's the first champion that a player buys, or at the very high ELO's where extremely good players have figured out how to actually make his damage output dangerous. In the mid tier ELO's, most discard the Rogue Mage in order to play mages with a larger range, like Morgana, or some other high burst champion like Annie or Anivia.
Relatively recently, Ryze has gotten a nerf that attacked the thing that made Ryze Ryze, his ability to scale massively off of mana, which would turn him into one of the very few legitimately beefy mages in the game.
This change modifies the number of builds otherwise expected on Ryze; instead of seeing him in the load screen and immediately counting down the gold to a Last Whisper, perhaps instead, a true AP Ryze may be in the making. Because while it is true that the former mana/tanky build for Ryze is still viable, it now lacks the characteristic ability to burst any champion from full to within 1/4 of health. However, that's not to say that the DPS is lacking in any way, it's just not as powerful as it once was.
But, now that the scaling is not so mana based, items that give AP are now worth more to the regular Ryze player while items that give both are now explicitly core ( Rod of Ages).
It also adds an interesting dynamic in which items that were otherwise off limits are now suitable; so perhaps a Hextech Revolver or Rabadon's Deathcap will become more common.
But, in my opinion, the most game changing item for the new Ryze is going to be Deathfire Grasp.
Deathfire Grasp has always been a great item, especially for high DPS burst mages that drop their payload and then sit and wait for their cooldowns to come off. But it's never really been a big deal for Ryze since it gave mana regeneration (Ryze had LOTS of mana), cooldown reduction (you get that from ionian boots, Frozen Heart, and Overload), and AP (AP on Ryze?). But with the recent changes to start transitioning him toward a more AP style of play, this item now fits very nicely. Now, it is acceptable to get Sorcerer's Shoes, a Frozen Heart, and Deathfire Grasp, for more DPS from magic penetration, and max cooldown reduction while making up for the hits to his base damage and scaling.
These are just a few of my musings and thoughts pertaining to Ryze in particular and since they have this free blog thing, I figured I would try it out with this. So, if you've taken the time to read this, I'm sorry. But otherwise, good luck on the Rift and Scar.