You could look through the dev notes on
http://www.bay12games.com/dwarves/ or look through last version's
Future of the Fortress thread. There might also be some stuff on the wiki, but I haven't really poked around there much, aside from the modding pages.
Movement speed and attack speed have been split into two. Before, they were tied together, so the slower you were, the slower you would attack. But now even if you are very slow, you can still attack based on the speed defined within the game files. Most attacks are the same speed though. Multi-attacking is now in as well, so you can make several attacks at once. Though some attacks are good for multi-attacking, and some are bad, while most are neutral. I don't know of any creatures other than the hydra that have good multi-attacks though, and kicking is usually flagged as bad.
There are also new movement states. Before, everything moved at a more or less constant state. Though swim speed and land speed were different, and they would be slowed by things such as crawling on the ground or sneaking. Now there are several movement states, with the default being walking. Units can go slower or faster than walking speed, and can even go into a full-on sprint. This is useful when dwarves are trying to run away from enemies.
There are also different speeds for different types of movement. Off the top of my head, there are different gaits for walking normally, crawling on the ground, swimming, climbing, and flying.
Sneaking has also changed. Before it would slow you down and you could only attempt to sneak when there were no hostiles within sight. Now whether you get slowed by sneaking depends on what type of movement state you are in, and you can attempt to sneak anywhere. Though that won't help much if your enemy can already see you.
There is also the new ability to climb, which can help stuck dwarves and makes fortress defence a bit harder.
Bandits can now attack your fortress, if they are nearby. Before they were an adventure mode only type of thing.