To the best of my knowledge there are only two changes to sectopods, although these are significant:
- They take half damage, i.e. effectively they have double their previous health
- Like other enemies that do not use cover, they can enter Overwatch on the "free" turn when they are discovered.
However, some changes to XCOM abilities make them more difficult targets:
- The heavy's HEAT ammo now only grants a 50% bonus against robotic enemies (previously 100%)
- The sniper's Squad Sight shots can no longer crit (which used to be rather frequent with Improved SCOPE against an enemy out of cover)
So the Sectopod has (effectively) more health, and XCOM's solidiers can put out less damage. On the other hand, there are a couple of new abilities that can help:
- The MEC's Electro Pulse will reliably stun sectopods for a turn, and probably kill any accompanying drones. An extra turn of the enemy not shooting back can often make up for the reduced damage that it takes
- A well-positioned Assault with Close & Personal can now get in three shots from an Alloy Cannon in a turn. While this can't kill a sectopod by itself, it can make a very large dent in its health!
There may also have been changes in the AI - anecdotally, it seems that sectopods are more willing to move than they used to be - but there's no way to be sure of this.