Runes Reforged is terrible for Riven.

The only real viable option now for her is play as an assassin and run electrocute.

Trying to play bruiser/slayer style riven is nigh impossible now without having fervor.

If you go into the defensive tree and build bruiser you do negative damage and if you go offensive tree bruiser you also do negative damage and are also squishy as hell.

Press the attack doesn't work with her unique combo based playstyle as by the time you proc it you can't take advantage of it and have to back off.

Losing out on the common runepage of 10% starting CD-R feels terrible and laning as her is equally bad now too.

The matchups you lost before you lose even harder and matchups you won before you have zero kill pressure on now. (Unless you cheese with aerie, but that doesn't scale well.)

I know it's just first impressions but the difference is immense compared to before and not in a positive way.