I think 'Google Duplex' is the biggest announcement from Google I/O 2018 as it is a big jump for Google AI from google assistant perspective. It was quite impressive to listen to Google assistant's natural dialogues with hair salon when she called to the hair salon on behalf of the user.
Besides that(1), (2) ANDROID P / (3) NEW GOOGLE ASSISTANT VOICES / (4) SMART DISPLAYS WITH GOOGLE ASSISTANT COMING THIS SUMMER / (5) GMAIL CAN NOW DRAFT EMAILS FOR YOU (ALMOST) BY ITSELF / (6) GOOGLE MAPS IS GETTING WAY MORE SOCIAL AND GOING AFTER YELP / (7) AND IT’S ADDING AUGMENTED REALITY DIRECTIONS / (8) GOOGLE PHOTOS GETS EVEN SMARTER EDITING POWERS / (9) GOOGLE NEWS — NOW CURATED BY AI were listed as top 10 biggest annoucements from Google I/O 2018 by Verge.
You can find the link here: https://www.theverge.com/2018/5/8/17328828/google-io-keynote-summary-highlights-news-recap-2018
Enjoy!