I have got to say that it made me so happy and nostalgic. Iris and Ash immerse themselves in a battle with the same intensity and that's why the battle was really great.
Emolga lighting up the stage for our new Unova Champion was a very nice detail. And I loved how cool Iris looked in her champion outfit. Not to mention Angrynite's coolness. Was so interesting seeing two Dragonite, yet two completely opposite ones. I also loved how she reacted when she saw Dracovish.
And Haxorus, finally Iris broke the "pokegirl has only cute pokemon" thing for one epsiode since XY. Haxorus is sick. I wish the battle would be a little longer because I felt like Dragonite and Haxorus were defeated a bit too quick, but at the end of the episode Iris said that she will try to reach the Super class fast so she can battle Ash again, so who knows.
One thing I didn't like was why they didn't show all her team. Excadrill, Gible and why show a Goodra in a flashback only to confuse us more (I will count Goodra as her team member tho). That's why would have been better if this was a two parter. Or if she returns for another battle they can show more team members then.
At first I was a bit disappointed from this episode, but after watching it again I can say it was overall very good. It's always nice to see companions return with achievements.
But still, May's return still holds 1st place, even thought Iris' return is right up there close.