Messages on iOS is changing a bit. Apple is adding rich linking for Websites and audio, and the camera launcher supports Photos and a live view of what you're up to.
Emojis are also bigger; that's huge (pun intended).
Maybe something that is cool are emoji predictions. Instead of just assuming what you want to type, iMessage also guesses what emojis you want to use. Words that can be changed to emoji are also highlighted, and you can switch to a tiny pic with just a tap.
Like Google's Allo, text can also be scaled to match a mood. Private messages are also obfuscated until the recipient swipes them; no more fear your significant other's friends will see your naughty text messages!
There's also a sketching feature for custom drawing, and you can send full-screen messages that pop away when tapped.
Pretty cool features, and not the Android support some were hoping for.
Developers will also have access to iMessage so they can make what amounts to bots. Instead of terrible conversations, though, you can do things like add stickers, GIFs or send money. Apps built for iMessage will show in a drawer inside of your Messages app, too.