Much difference from Ozone4??
limiter gains a new Intel mode and independent channel limiting which are both
different, harmonics work better. Verdict's out on the rest IMHO, some say that other modules have improved but I've only sat down and played with those two so far.
The new I3 mode has a more aggressive transient response saving design. Normally that would be awesome but I found a section of material where it caused it to pump and drop out for a split second so I went back to I2 instead for that. Tried it again without a compressor in the chain, same result (so it was the limiter, not something else), tried it with a different compressor in the chain and it sounds fine so whatever was in the original content has gotten smooshed/molded enough that it doesn't try and recreate something. The lesson is really that while I could consistently get good results with I2, I'm wary of I3 at the moment (when it works well, it sounds better to me though). The harmonic's module benefits from the new oversampling option.
The new UI is meh...
While there is some stuff in the advanced option, I don't think it's worth $1k for what we do. ymmv. There is a full list of changes on the product side (can't hotlink)