I like Ozone 4 better than Ozone 3. I don't like the EQ or MB comp much on it, I think they can get a bit harsh quickly, but again I think 3 was worse in this regard over 4. I like the harmonic exciter and limiter, though.
IME, their support sucks ass, though. I've sent 4 emails since I moved to Windows 7 trying to get them to register my Ozone 4. I wanted to move it to my iLok (it was previously unlocked through call and response when I installed on Vista) to not have to mess with it in the future, but it won't let me since I registered on their site through the other method, and they've never answered 1 email to help. Everytime I try to do anything with the serial, I sign in on their site and try to register Ozone 4 and move to iLok, it says the user and pass already exist (obviously, because it's mine), and to contact admins for help.
I ended up downloading a call and response crack from Ozone 3 and adapting it to Ozone 4. Luckily, it worked.