First, the HTML5 exporter. <img src="smileys/smiley4.gif" border="0" align="middle" />
Then, physics. Especially joints. They open lots of amazing possibilities.
Finally, short descriptions of events, actions, and action parameters. A small but really useful feature.
Needless to say, Construct 2 is a great application as a whole. I can't wait for more great features. And yes, a Scirra's tweet led me to this thread. <img src="smileys/smiley17.gif" border="0" align="middle" />