Understanding The WordPress 4.2 & 4.2.1 Update For Business Owners and made easy! This update features a few main things:
- A critical security update (4.2.1)
- Improved backend API
- Non-English character support for Asian languages (this also includes official support for Emoji)
- Improved plugin management (same-screen install and update)
- Improved embedding support
- Slight admin color change (it's a good change I think)
- Revamped Press It feature.
And of course some other smaller bug fixes, security bugs squashed and issues resolved and even functionality improved (in the backend).
You can learn more about it on the official WP release page: https://wordpress.org/news/2015/04/powell/