The Almond 3s is more closely like the Almond 3. I think there are some comparisons between that and the Almond+ floating around in the forum.
The two biggest IMO:
1) Mesh networking capability. Not something most people worried about previously. But with the proliferation of devices that need a wifi signal around a house, dead spots and underused areas (like basements) now need a connection.
2) The Z-Wave dongle. Means that as Z-Wave progresses, you can put in a new dongle to benefit. I now have a Z-Wave Plus dongle in my Almond 3 (which I would use with an Almond 3S). The Almond+ does not have Plus, it was not available yet. It also makes it possible to have the same Almond 3 shipped to many countries. Just plug in the country-appropriate dongle. More a benefit for Securifi than me personally. But it also means customers globally can just get ANY Almond 3 (or 3S when it arrives) and plug in the dongle they need rather than worrying about whether there will be a 3S for their market (like there was with the Almond+ during the Kickstarter, people wondered if it would be available for X region).