For one thing, users can now offer star ratings and feedback for developers for these bots, just like they can with apps. There's also a new feature called Quick replies, which are essentially buttons that refer to the bot's most recent messages, thus allowing for faster conversations. So, for example, it might ask you to pick a color of a hat and simply offer "Red" or "Green" as the two Quick reply options. Bots will also now have the option of persistent navigation options in the window itself, just in case you forget a text command.
There'll also now be an account linking option that'll let businesses connect their customers' accounts with their Messenger accounts. You could then hook up your account at, say, 1-800-Flowers, with your Messenger account for more personalized service. Facebook says it's a secure protocol, but rest easy, security-conscious; account-linking will be opt-in.
Last but not least, bots will now have the option of sending GIFs, video, audio as well as files. If you're interested in learning more about new Messenger bots, Facebook has also announced a new Messenger blog that'll feature more about the up-and-coming platform.