Reading between the lines, defamation law still applies. It is only extra clauses in the sales contract banning/punishing bad reviews which are now not allowed.
If I write that I bought a new Rolls Royce, but when it arrived it was made of cardboard, and when I sat in it it collapsed and then caught fire, I can still be sued for libel, and if RR can show I was lying, I'll lose. Conversely if RR habitually sues people who post honest opinions which criticize them, then they're open to a SLAPP countersuit. This looks like a good balance to me.
Note, I am not a lawyer, and have no information beyond reading TFA. Corrections and elaborations from actual lawyers are welcome.