Right now Reina (Sombra) and Yun (Mei) are finished, Aurelie's (Widow) route is not finished but had a satisfying conclusion to her ark, so that's worth a play too.
Next month Freja (Brigitte) will be getting an Epilogue to her route, although the main story line is technically also done. And Ava (DVa) will be getting a Finale at the beginning of next year!
Right now we are working on an Overhaul Update, which we will push to release next year. It will include LOTS of changes, and since it's so huge that's why it requires so much time.
So if you are a free player — wait for Aurelie's (Widow) Part 4 to go public and play the game, which should happen in around 2 weeks.
Right now it's probably the best time to play to truly appreciate the Overhaul Update once it goes live.
In regard to patch that will revert the changes to their design, sadly we can't do that due to potential legal issues. That being said, Reina's redesign was the only one that you can call somewhat drastic, with the rest of the cast receiving only minor adjustments. On top of that, we will revert some of the changes to Reina's design to bring her closer to the look our players are familiar with.