The new dropper block will come in useful alongside the hoppers, as it places items into chests when it receives redstone current. Speaking of hoppers, more than a dozen bug fixes mean that they should be working much better now and minecarts can now be constructed that have hoppers built in. There's definitely a few puns to be made here, but I am a man of restraint and I will not be baited.
Both skeletons and zombies have been made tougher opponents, with skeletons now harder to hit in combat and zombies now better at avoiding arrows. This scales according to the difficulty you're playing at. New chat options have been added and quartz columns can now be built sideways.
Be warned: a few redditors are already reporting a bug with this snapshot. It appears the new dropper may spawn infinite copies of whatever item you place in it. Creating a new world appears to rectify this problem.
UPDATE: It looks like Dinnerbone has already fixed this bug and any new downloads of the snapshot shouldn't contain it. That's pretty speedy work.
The snapshot can be found on Mojang's site and if you've never tried downloading and installing one of these developer snapshots before, we just happen to have written a short how-to that you may find helpful.