They made it so the turrets can no longer run out of ammo which should make the laning phase a bit more involved. They also changed the way the health globes which drop from the spellcaster minion works. So before the globes were always tied to one team who could get it. Now its tied to the same team as before for the first 3 seconds but then becomes neutral and able to be collected by either side. This should make winning a lane more useful as you can deny them their globes AND take the globe for yourself.
On a side note, I find the most interesting change with HotS is they are introducing performance based ranking where while its still mostly win/lose for gaining/losing MMR, now it actually takes into account how you performed personally for how much you might gain or lose. Assuming it works pretty well it could be a huge step in the right direction for how it feels to play super well in a loss and in general could help solid players climb a little faster by mitigating their losses a bit from their own good play.