Biggest thing is this:

We’ve eliminated the requirement that disputes be resolved by individual arbitration. As always, we encourage you to contact Steam Support when you have any issues, as that will nearly always be the best way to reach a solution. But if that doesn’t work, the updated SSA now provides that any disputes are to go forward in court instead of arbitration. We’ve also removed the class action waiver, as well as the cost and fee-shifting provisions, that were in prior versions of the SSA.